Special Report: Automotive Electronics + Infotainment

December 2019

Special Report: Automotive Electronics + Infotainment (pg 19)

VIEWpoint

Recharging the BatteriesBy Ally Winning, European Editor, PSD

DESIGNtips

Power Your PLC with a Small POL ModuleBy Nazzareno (Reno) Rossetti & John

Woodward, Maxim Integrated

MARKETwatch

The Future Looks BrightBy Kevin Parmenter, Field Applications

Manager, Taiwan Semiconductor

COVER STORY

Maintaining SiC MOSFET

Efficiency and Protection

without Compromise

By Thorsten Schmidt, Technical Product Manager, Power Integrations

TECHNICAL FEATURES

Energy Efficiency

Shane Timmons, Product Marketing Manager, Diodes Incorporated By Shane Timmons, Product Marketing

Manager, Diodes Incorporated

Smart Power

Smart Power Solutions for Data Centers Cut Operating CostsBy Ali Husain, ON Semiconductor

SPECIAL REPORT:AUTOMOTIVE ELECTRONICS + INFOTAINMENT

Implementing Fast DC BEV

Chargers Up to 150 kW

By Omar Harmon, Francesco Di Domenico and Srivatsa Raghunath, Infineon Technologies

Electronic Pervasiveness in

Vehicles Brings EMI Challenges

By Felix Corbett, TTI Europe

Designing for a Safer Future

Mike Branch, Vice President Data &

Analytics, Geotab

Battery Monitor Maximizes

Performance of Li-Ion Batteries

in Hybrid & EV

By Cosimo Carriero, Analog Devices, Inc

Improving Mild Hybrid EV Power

Supply Systems with High Step-

Down Ratio DC/DC Converters

By Satya Dixit, Sr. Director of Solution Mktg & App, ROHM Semiconductor

2

FINALthought

When Less is MoreBy Ally Winning, European Editor, PSD

Dilbert

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Highlighted Products News, Industry News and

more web-only content, to:

www.powersystemsdesign.com

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13

40

COVER STORY

Maintaining SiC MOSFET Efficiency and

Protection without Compromise (pg 6)

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POWER SYSTEMS DESIGN

Welcome to the final edition of Power Systems Design of the year, and in fact, the decade. It has been a mixed year so far, with plenty of innovation on display, but a flat economy putting a bit of a spoiler on the industry. The forecast for next year is pretty mixed too, with some people predicting a global recession. As the old saying goes, economists have predicted eight of the last three recessions, so let’s keep our fingers crossed they are wrong this time as well. One thing’s for sure, even a flat market won’t stop the rate that new innovations appear.

The holiday season is a perfect time to recharge the old batteries and set you up for a new year. And next year there will be plenty of batteries getting recharged, both human and physical. There are electric vehicle infrastructure projects ongoing in most advanced countries. Government would love to change over from combustion engines sooner rather than later, but that won’t happen if the infrastructure doesn’t support the changeover. It’s not just the number of physical charging points that are required, the convenience of charging has to become much more like filling a car with petrol to persuade the majority of people to make a switch. Many drivers only do short journeys and could get away with charging their vehicles overnight, but on the, often rare, occasions they wish to make longer journeys, a similar experience to a petrol pump is needed. For business travellers that convenience is an absolute necessity.

Luckily electronics companies have been working extensively on just that problem. Inside this month’s magazine, Omar Harmon, Francesco Di Domenico and Srivatsa Raghunath from Infineon Technologies get together to tell us how the company’s technologies can work together to provide a modular approach that provides 200km worth of charge in around 15 minutes. The technology keeps costs down by using the same building blocks to create solutions for the different standards implemented around the world. SiC plays an integral part in those solutions, and they possibly wouldn’t even be feasible without the new material.

SiC allows us to switch high currents much more quickly. Faster switching means smaller magnetics are required, providing more compact, and importantly for electric vehicles, lighter solutions. Faster switching also introduces EMI challenges for the vehicles. Electric vehicles rely a lot more on electronics than conventional vehicles, and EMI generation can interfere with the other electrical circuits in the vehicle. This means designers have to be aware of the problems and incorporate solutions throughout the design process. In our second special report article this month, Felix Corbett from TTI looks at these challenges and the techniques and components that can minimise EMI disruption, while surviving in the challenging conditions that automobiles offer.

I hope you enjoy the issue, and the whole PSD team wishes you and your families a very Merry Christmas and a Happy New Year. We’ll be back next year with many more great technical features.

Best Regards,

Ally Winning European Editor, [email protected]

Recharging the

BatteriesPower Systems Corporation 146 Charles Street Annapolis, MD 21401 USA Tel: +410.295.0177Fax: +510.217.3608 www.powersystemsdesign.com Editorial Director Jim Graham [email protected]

Editor - EuropeAlly [email protected]

Editor - North AmericaJason [email protected]

Editor - ChinaLiu [email protected]

Contributing Editors Kevin Parmenter, [email protected]

Publishing DirectorJulia [email protected]

Creative Director Chris [email protected]

Circulation Management Sarah [email protected]

Sales Team Marcus Plantenberg, [email protected]

Ruben Gomez, North America [email protected]

Registration of copyright: January 2004ISSN number: 1613-6365

Power Systems Corporation and Power Systems Design Magazine assume and hereby disclaim any liability to any person for any loss or damage by errors or ommissions in the material contained herein regardless of whether such errors result from negligence, accident or any other cause whatsoever.

Free Magazine Subscriptions, go to: www.powersystemsdesign.com

Volume 16, Issue 10

Power Your PLC with a Small POL ModuleBy: Nazzareno (Reno) Rossetti & John Woodward, Maxim Integrated

The vision of the smart factory is a reality in many industries, thanks to advance-

ments in automation and data exchange in manufacturing tech-nologies. Factory floors are filled with controllers, sensors, I/Os, and actuators. A controller can be a pro-grammable logic controller (PLC, Figure 1), motor/motion control-ler, or a distributed control system (DCS) using advanced processors and microcontrollers. Sensors can be either digital or analog and used for proximity, vision, weight, or tem-perature. Actuators can be robots, valves, motors, computerized nu-merical control (CNC), contactors, and other moving mechanisms. Inputs and outputs (I/Os) can be digital or analog or even universal I/Os that connect sensors and actuators to controllers.

Figure 2 shows a PLC or an indus-trial computer that monitors and controls a single manufacturing process. It includes a processor, I/O modules, memory/program-ming, and a power supply. The 24V field bus is bucked down to 5V with the flyback converter, a transformer-based architecture that isolates the PLC module from the harsh industrial electrical environment. The flyback output is converted

down to the necessary PLC voltage rail by the POL voltage regulator. PLCs and other control systems are orchestrated by software packages like SCADA (supervisory control and data acquisition), monitoring and controlling multiple interfaces and peripherals.

The PLC receives inputs from sensors on the factory floor, processes them locally, and drives the proper actuators. Today’s sensors, I/Os, and actuators are equipped with internal processors that make simple decisions lo-cally without the need to escalate to the control-

ler, thereby improving throughput. Unless multiple devices need to be considered, the PLC is not even involved. By networking the data generated by all the equipment to the cloud, analytics can be run in real time using advances in AI to determine the action to be taken.

Figure 1: Programmable Logic Controller Module

Figure 2: PLC System Monitors and Controls a Single Manufacturing Process

DESIGN t ips


4

DESIGN t ips


The ChallengeThe proliferation of processors and connectivity interfaces into every controller, sensor, I/O, and actua-tor on the factory floor, places new requirements on system hardware: reduced component size to fit additional electronics in the same chassis, improved energy efficiency to perform within the same or lower thermal budget and increased electrical/mechanical safety and reliability to reduce downtime.

A module approach to the voltage regulator powering the PLC, where the inductor is mounted vertically on top of the IC, reduces the solu-tion BOM, footprint and improves reliability and time-to-market. The voltage regulator module POL, must also be efficient to reduce heat generation, further improving

system reliability.

In this design solution, we review a typical module approach to pow-ering the PLC and present a new solution that is cost effective and superior in efficiency and size.

Typical POL Module A PCB layout for a typical synchro-nous 5VIN, 1A switching regulator module is shown in Figure 3. The confinement of the inductor results in a reduced footprint of 16.6mm2.

uSLIC POL ModuleThe uSLIC™ module in Figure 4 supports up to 1A load current and allows use of small, low-cost input and output capacitors. A reduced module size (2.6 x 2.1 mm2 vs. 2.6 x 3 mm2).and a reduced BOM (5 components vs. 4 and in a smaller size) results in a cost-effective solution and footprint net area of 11.8mm2 or 29% smaller than the typical solution.

The output voltage can be adjusted from 0.8V to 3.3V. The module sig-nificantly reduces design complex-ity, manufacturing risks, and offers a true plug-and-play power supply

solution, reducing overall time-to-market.

Efficiency AdvantageFigure 5 compares the efficiency of the two solutions. The generic solu-tion (red curve) is ill equipped at light load, where the efficiency drops dramatically, and at full load it falls short of 3% points.The uSLIC module has high efficien-cy across the entire range of opera-tion (green curve), making it ideal for line-powered as well as power-stingy battery-powered applications.

ConclusionThe smart factory relies on a pleth-ora of sensors and actuators placed across the factory floor. The informa-tion is processed by PLC modules powered by voltage regulator POLs. A modular approach to the POL reduces system BOM, improves reliability and time-to-market. In this design solution, we reviewed a typi-cal POL and compared it to a novel approach that yields a module that is smaller, has higher efficiency, and is more cost effective.

Maxim Integratedwww.maximintegrated.com

Figure 3: Typical Solution Net Area of 16.6mm2 for a Switching Regulator Module

Figure 4: Improved Solution Net Area 11.8mm2 using a uSLIC POL Module

Figure 5: Efficiency Comparison Between the uSLIC Module and Competition

According to Markets and Markets the in-vehicle infotainment market will reach 30.47

billion USD in 2022, at a CAGR of 11.79%. Consumers want luxury, comfort, connectivity and conve-nience with them everywhere. Not long ago, I read about customer expectations created by the user interfaces in consumer electronics being advanced yet easy to use and intuitive. When these same con-sumers went to work and confront-ed equipment in their workplaces such as laboratory test equipment or medical instrumentation, CAD-CAM, PLC’s –industrial equipment and the like and the user interface looked like a commodore 64 run-ning fumble-ware software. The users pushed back. “Why does my phone or TV have a great intui-tive GUI and I bought it at Costco, and we bought this 500-thousand-dollar instrument at work and the interface looks like its 1985?” Even-tually companies adopted modern RTOS on single board computers or Android or Linux, color LCD displays and so forth to fix this. The same goes for the automotive industry, customers expectations for consumer electronics transfers to automotive applications. What’s driving the automotive telematics

The Future Looks Bright

By: Kevin Parmenter, Field Applications Manager, Taiwan Semiconductor

and infotainment market? The electrification of transportation combined with increased focus on passenger comfort and safety and of course global regulatory standards for safety. The trans-formational trends in electronics industry overall are converging to transform the infotainment and automotive market. Namely - Autonomous driving, 5G, AI, sensor fusion, the electrification of transportation and environ-mental concerns. Infotainment benefits from AI to improve the user experience and autonomous driving needs AI as an enabler. Infotainment AI goals are all about advancing the intuitive user experi-ence and human interface – easy to use features and functions. Au-tonomous driving goals are safety, reliability, redundancy with lots of sensors being used, Fast Startup and response to human and sensor inputs, central data storage includ-ing consumer entertainment files, dashcam video, Event Data Record-er and OTA – (over the air software updating) from Wi-Fi or 5G Cellular interface, continuous connectivity (5G) protected with cybersecurity to prevent malicious hacking and so forth. Major automotive compa-nies have stated no more combus-tion engines by X date, so electric

is here to stay. For us in the power electronics industry this is very good news. Everything mentioned needs more and more power pro-cessing, protection from transients and surges, POL with sequencing of supply rails, Rohs compliant parts and more. The power elec-tronics requirements range from in the vehicle electronics of all power levels to infrastructure power such as the 5G network, charging sta-tions for the EV and sensors of all types. The opportunity ranges from the semiconductor devices to modules and components of all types including the passive electro-mechanical components and com-plete power supplies, subsystems and converters – inverters, test and measurement equipment and more. It appears that the automo-tive market by itself is justification for wide bandgap power semicon-ductor adoption. The automotive market will drive the ecology of drivers, test equipment, controllers, co-packaging and device reliability, quality, volumes and pricing which will allow other industries to adopt WBG parts as common practice. The solution has finally found a problem to solve! Full speed ahead!

PSDwww.powersystemsdersign.com

MARKETwatch


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COVER STORY

WWW.POWERSYSTEMSDESIGN.COM WWW.POWERSYSTEMSDESIGN.COM


Maintaining SiC MOSFET Efficiency and Protection without Compromise

By: Thorsten Schmidt, Technical Product Manager, Power Integrations

The efficiency and size benefits of SiC devices have been embraced by designers of industrial, automotive, traction systems and photovoltaic power conversion

The lower sheet resistance of wide-bandgap SiC materials (typically 1/100th that

of conventional silicon) results in smaller devices for a given current capacity – valuable in space saving applications. In addition, the electric-breakdown- field for SiC (approximately 2.8 MV/cm) allows for a much shorter isolation region within the material. A significant benefit is that the smaller size of SiC switches reduces parasitic capacitance, which improves switching efficiency and allows the switch to operate at higher frequency without penalty. These are clear benefits however, the reduction in the mass of the switch means that protection circuitry has to operate very quickly in order to prevent thermal damage. Shutdown in less than 3 µs is a common requirement for SiC devices (as compared to the 10 µs seen with conventional IGBT and MOSFET switches).

SiC technology is relatively new in the mainstream, and there are different device structures being used as the MOSFET designers

work the new material. Cascode and MOSFET configurations with different gate characteristics have resulted in a wide range

of gate voltage requirements, further challenging the circuit designer. As with all switches, protection circuitry is required to safely turn off the switch in the event of a system short-circuit. Desaturation detection must avoid false tripping and this typically results in a switch blanking time of up to 2 µs – a significant portion of the thermally limited high current

time envelope. Fast turn off (rapid di/dt) may induce VDS overvoltage during shutdown so shutdown rate must also be controlled.

Figure 2 shows a typical gate drive circuit for an IGBT switch and associated short circuit shutdown characteristic. During a short circuit shutdown, VCE rises above the DC Link voltage

and causes the TVS network to break over delivering current Iac to the gate node. Iac2 charges Cres and causes the gate voltage to rise and turn the switch back on to limit VCE. However switch T2 pulls current Iac1thru gate resistor Rg(off ). Increasing Iac3 (via ACL pin) increases the impedance of T2 and reduces Iac1 , but this takes time. The solution is to increase the gate resistance, which will reduce the current drain from the gate node and improve the clamping voltage. Driving and IGBT in this way is effective and the change in gate resistance does not significantly change switch efficiency. However, increasing gate resistance for a MOSFET will reduce switch transition speed, increase switching losses and reduce efficiency.

To safely and quickly shut down an SiC Switch without increasing gate resistance requires a different detection and shutdown

Figure 1: Comparing SiC with conventional Silicon MOSFETs reveals the clearly superior semiconductor characteristics of the SiC material, which allows the construction of significantly smaller switching devices.

Figures 2a (left) & 2b (right): IGBT Desaturation Detection and Advanced Soft Shutdown in Operation. IC increases and induces a shutdown (VGE reducing). Subsequent overvoltage (VCE) detection causes an increase in VGE to limit voltage overshoot and complete a safe shutdown of the switch by limiting di/dt.

Figure 3: SiC advanced Active Clamping: Toggling current to the gate via T4 and T5 provides a very rapid shutdown while providing an aggresive control of VGS to limit the VDS excursion. Following a 1.3 µs blanking time a desturation-fault shutdown asserts allowing the SiC MOSFET to be turned off in less than 1.8 µs. The toggling of the VGS gate drive can be clearly seen

8

COVER STORY


strategy. Figure 3 Shows an SiC Switch short circuit shutdown using a new control algorithm to provide rapid and controlled switch shutdown.

As before the desaturation triggered shutdown induces a VDS overvoltage to occur, this causes the TVS stack to break over. Iac2 charges Cres. As before,

Iac1 begins to flow thru Rg(off ) reducing Iac2. However, in this configuration Iac3 induces a rapid response from the IC control logic. In this case the control circuitry rapidly toggles T4 and T5 to alternately sinks and sources Iac1 current. This strong drive reduces effect of Rg(off ) on Iac2 making an adjustment in gate resistance unnecessary. This allows fast turn-off and control of VDS without compromising efficiency.

By removing the role that the gate resistors play in limiting voltage overshoot, the SiC

advanced Active Clamping employed in the SiC SCALE-iDriver™ IC family from Power integrations allows the designer to optimize the gate drive resistors to maximize efficiency without compromising performance to insure safe shutdown protection.

How is the gate driving challenge being addressed? Figure 4 shows typical gate voltage regions for different SiC switch structures. Some devices require a regulated

Figure 4: Turn on and Turn off requirements for different SiC switch types. The requirements are often mutually exclusive – making the design of the ‘universal SiC gate driver’ more challenging

Figures 5a (top) & 5b (bottom). A SCALE-iDriver power transformer provides 15 V to the VISO pin and the control IC uses an internal regulator to generate a stable drive voltage, as directed by the bias input. Additional circuit modifications may be required to reduce potential circuit oscillations during turn-on which will be switch dependent

turn-on voltage while others need a regulated negative turn-off voltage to ensure that they do not exceed the gate-source safe operating area as given in their respective data sheets. Typically, only one voltage can be regulated, while the other voltage is dependent on actual load conditions.

To create a stable gate-driver control voltage, various controllers use bi-polar or unipolar supply voltages to provide an isolated driver voltage. A unipolar-based gate driver is shown in figure 5. The power supply delivers a raw supply voltage to the VISO pin of

the control IC. In order to match the requirements of a particular SiC MOSFET, an external programming input is required. A gate driver bias circuit is used to adjust the centre point of the drive rails (delivered via the GH and GL pins). A potential divider between VISO and COM pins is used together with a shunt-regulator to control the drive voltage partitioning via the VEE pin. The shunt regulator provides a more temperature and load stable voltage than would a simple Zener diode based solution.

Driving silicon carbide MOSFETs provides significant

challenges for the gate-driver circuitry. Traditional control techniques are often inadequate – unable to support the rapid switching and corresponding overvoltage control issues that follow a desaturation (short circuit) event. In addition, the nascent nature of SiC switch design means that there is wide variation in gate-drive voltage requirements. Solutions exist that can provide the rapid control and meet programmability without compromising efficiency or safety in switching circuits.

Power Integrationswww.power.com

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1110

ENERGY EFFICIENCY



Super Barrier Rectifiers Deliver Design-Free Efficiency

By: Shane Timmons, Product Marketing Manager, Diodes Incorporated

The Super Barrier Rectifier can be utilized in the same way as a Schottky diode while delivering significant and instant gains for a range of applications

Successive generations of power-semiconductor devices based on existing technologies

strive to deliver incremental improvements in energy efficiency. Now there is a device, realized through proprietary technology, that enables power supplies to achieve a significant leap forward in performance and efficiency—the Super Barrier Rectifier (SBR).

Maximising power efficiency has become a key concern for designers of almost all types of electrical and electronic systems, such as mobile and smart appliances, automotive electronics, building automation, and data centres. In addition to improving energy ratings, greater power efficiency can also allow simplified thermal management, reduced size and weight, and longer battery runtime.

Focus on Automotive LightingThe automotive sector is experiencing a wholesale shift towards LED-based external lighting, not least because it can

deliver a reduction in electrical power consumption in vehicles. With the increased awareness of the need for energy efficiency, hybrid and electronic vehicle characteristics as well as the subsequent link between electronic power and fuel economy--or driving range--is becoming more widely understood.

To encourage even wider market appeal, the industry is constantly seeking to further improve the efficiency of LED lighting systems

and, in particular, Daytime Running Lamps (DRLs). As DRLs remain on continuously while the car is running, predominantly as a safety feature, they have also come to define the signature look of certain models and brands. As an ‘always on’ feature, one way to improve LED DRLs is to tackle the efficiency of power-conversion that takes place in the LED driver/controller circuitry.

A buck-boost topology is typically used in automotive applications

to provide DC-DC conversion for various applications, including the drive voltage required for the LED string. Figure 1 shows a simplified circuit featuring the ZXLD1371 buck-boost LED driver/controller from Diodes Incorporated. This is a generic circuit that normally contains a switching MOSFET (Q1) and a freewheeling diode (D1).

Because this is a boost converter, the peak current in the MOSFET and freewheeling diode is much greater than the average LED current, hence the conduction and switching losses of these two components can have a significant impact on the overall converter power consumption.

Historically, Schottky diodes have been selected as the most efficient option due to their lower forward voltage drop (VF) and faster switching capability compared to conventional rectifier diodes; however, reverse leakage current is relatively high and increases with temperature.

While the Super Barrier Rectifier (SBR) behaves like a Schottky diode, the SBR delivers higher efficiency when used in switching converters, and although its con-struction means that the forward voltage and reverse recovery time are comparable, leakage current is much lower and more stable with increases in temperature. The avalanche capability is also signifi-cantly higher, leading to greater ruggedness. Table 1 compares the key parameters that govern

freewheeling performance for an SBR and Schottky diode with similar reverse-voltage and current ratings.

SBR Under the SkinSBR is a proprietary and patented Diodes Incorporated technology fabricated using a Metal Oxide Semiconductor (MOS) manufacturing process. The presence of the MOS channel forms a low potential barrier for majority carriers, resulting in forward-bias performance similar to that of the Schottky diode at low voltages. However, the leakage current is much lower due to overlapping P-N depletion layers and the absence of potential barrier reduction.

The SBR is represented by the same electronic schematic symbol as the Schottky diode. In practice, the internal structure is like a MOSFET with the gate and source terminals connected together creating the SBR anode terminal. The MOSFET drain acts as the SBR cathode.

Other than displaying lower leak-age with superior temperature stability and avalanche capability, an SBR behaves like a diode in any circuit, and as such it is a drop-in replacement for comparable Schottky devices. Without needing to redesign a PCB or add addi-tional components, the SBR deliv-ers immediate improvements in efficiency and a reduction in device case temperature that enables simplified thermal management and greater reliability.

Higher Efficiency, Cooler RunningTable 1 compared the SBR and Schottky diode in identical buck-boost DRL power supplies con-trolled by the ZXLD1371, as shown in Figure 1. The SBR shows a significant efficiency advantage, increasing at higher ambient temperatures where the Schottky circuit efficiency reduces by as much as 6%, as shown in Figures 2 and 3.

Plotting the efficiency of both circuits against ambient temperature (Figure 4) shows

Figure 1: Simplified Schematic of Buck-Boost LED Driver for DRL Application

Table 1: Comparing the Diodes Incorporated SBR with a Typical Schottky Diode

12

ENERGY EFFICIENCY


that the efficiency reduces with temperature due to a combination of increasing diode VF, leakage current, and switching loss, as well as overall system losses. The SBR’s superior temperature stability minimises this loss of efficiency compared to the Schottky-diode circuit.

The SBR’s superior efficiency delivers a twin benefit, both sav-ing energy and resulting in lower device operating temperature. Figure 5 shows how the SBR case temperature is consistently about 5°C lower than that of the Schottky diode across the full ambient-temperature range. This

lower temperature allows the DRL designer greater freedom to man-age heatsink size and cost while also achieving the desired system reliability.

Drop-In Upgrade from 10V to 300VThe Q series of SBRs, including the SBR10M100P5Q, are opti-mised for automotive applica-tions; however, Diodes offers SBRs covering a wide variety of voltage ratings and package styles to de-liver efficiency and reliability ad-vantages for other sectors, such as industrial, consumer electronics, communications, and computer systems, and with environmental technology, such as bypass-diodes in solar panels. Extremely low VF minimises temperature rise to maintain system reliability, and the devices have a wide operating temperature window that ensures compliance with the solar-industry safety standard IEC 61730-2.

Devices in higher voltage ratings, up to 300V, are suited to appli-cations such as switched-mode power supplies (SMPS) and solar inverters. In addition to superior efficiency and cooler surface tem-perature, SBRs have high surge-current ratings to withstand haz-ards, such as unpredictable power flow and lightning strikes.

ConclusionIn today’s energy-conscious and efficiency-focused world, the SBR enables a valuable step-change in power conversion performance. With reduced leakage current,

Figure 2: Efficiency Comparison at 25°C Ambient Temperature

Figure 4: The SBR Efficiency Advantage is Greater at Higher Ambient Temperatures

Figure 5. Lower SBR Case Temperature eases Thermal Management and De-sign for Reliability

Figure 3: Efficiency Comparison at 85°C Ambient Temperatureimproved switching performance, comparable or lower VF, and outstanding temperature stability, the SBR offers superior efficiency without any additional design effort to deliver a reduced time to market for numerous applica-tions. With the added advantage of cooler operating temperatures, power converters for systems

covering automotive LED lighting, consumer adapters, and renew-able energy systems can deliver superior performance and reli-ability while meeting the latest eco-design objectives and safety standards.

Diodes, Inc.www.diodes.com

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1514

SMART POWER



Smart Power Solutions for Data Centers Cut Operating Costs

By: Ali Husain, ON Semiconductor

Designers can now create sophisticated power solutions for data centres that are efficient, compact and reliable

As a society we are creating, using and sharing unprecedented amounts of data every

single day, both in our personal lives and while we work. In addition, the Internet-of-Things (IoT) which connects billions of devices and is growing, is creating data completely unaided by humans. As mobile technology moves into its fifth generation (5G),

capacity will exist for more data to be created and moved more rapidly than ever before, adding even more momentum to the trend of data growth.

All of this data needs to be stored somewhere, for processing and record keeping. Increasingly, we are turning to the ‘cloud’ for the safe-keeping of this vital information. However, the ‘cloud’

is not some ethereal place, it is very firmly rooted on terra in the form of the huge data centers that are rapidly growing in size and number to cope with the incessant demands for additional storage capacity.

Not surprisingly, data centers require significant amounts of electrical power to operate. Currently, it is estimated that they

consume around 3% of electrical power within the US, although this is expected to rise to a remarkable 15% over the next two decades. There are in excess of ten million servers shipped each year, and this number is continuing to grow at around 5% every year to meet the growing demand from emerging applications including VR/AR, artificial intelligence (AI) training and the IoT.

Power efficiency and reliability is probably the most important topic within the data center industry as physical space is at a premium, electrical energy is rising in cost and system reliability is paramount. As efficiency is increased, so operating temperatures fall which, in itself, improves reliability. This also allows power solutions to become denser, saving space – or allowing more computing power and storage capacity to be fitted into the available space.

Despite designing for reliability, components with moving parts such as disc drives and fans will wear and possibly fail during the operational lifetime of the data center, and therefore power systems must be designed to allow for hot-plugging / swapping of these devices so that repairs (and upgrades) can be performed without incurring system downtime.

Technology provides the solution to the power challengeIn order to meet the challenges posed by data centers, power solutions have to become smaller, denser, more efficient and more sophisticated.

MOSFET technology has improved significantly, allowing the integration of a control IC and MOSFETs in a very efficient and compact package.

For example, ON Semiconductor’s NCP3284, DC-DC converter has

a 30A continuous (45A pulse) capability all within a tiny 5mm x 6mm footprint and, with its ability to operate at frequencies up to 1MHz, the size and weight of external inductors and capacitors can be reduced. This integrated device also includes multiple protection features and programmable soft start.

At the next level of power density are smart power stage (SPS) solutions such as the FDMF3170. These integrate MOSFETs with an advanced driver IC plus current and temperature sensors allowing the design of high current, high frequency, synchronous buck DC-DC converters.

This fully integrated approach allows the SPS to be optimized for driver and MOSFET dynamic performance, system parasitic reduction and MOSFET on-resistance. The FET pair is optimized for the highest efficiency, especially at low duty cycles where modern efficiency requirements such as 80 plus are very stringent.

Highly accurate current monitoring (IMON) can be used to replace inductor DCR or resistor sense methods, thereby eliminating the losses usually associated with such approaches.

In modern data center server systems, even the humble fuse has had a makeover. Essential in applications such as RAID systems, disk drive power and server I/O cards, the fusible wire Figure 1: Multiphase controllers and DrMOS power stages provide solutions

Figure 2: Wide bandgap materials comparison

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SMART POWER


in a glass cartridge is replaced by an intelligent, semiconductor-based eFuse. eFuses use low on-resistance MOSFETs to protect peripherals during normal operation and while hot-swapping is taking place. In fact, they can be used in any application where power glitches or load faults may occur, as well as where inrush / outrush current may require limiting. In addition to providing protection to components, connectors and PCB traces, they are able to be controlled by the system and many can provide useful telemetry features such as monitoring temperature and current.

ON Semiconductor’s NCP81295/6 hotswap controllers support currents up to 60A peak (50A continuous) and are based on a 0.8m Ohm internal MOSFET for efficient operation. Housed in a 5mm x 5mm 32-pin QFN package, they offer a latching

off or auto-retry version and are suitable for use at temperatures up to +125°C.

Another eFuse - the NIS5021 is a 12V, 12A series device that is often used with hot-pluggable hard drives. It buffers the HDD from any excessive input voltage that could damage sensitive circuitry. An inbuilt voltage clamp limits the output voltage to protect the load, while maintaining a continuous power feed meaning the drive can continue to operate normally.

Complex systems such as servers often require intelligent control of their power systems to ensure proper operation as well as the highest possible levels of efficiency. Load management devices allow power rails to be segmented, thereby enabling granular control. This facilitates power sequencing at startup and reduces operating costs by permitting unused sections of

the circuit to be powered down. In turn, the lower power levels result in less heat in the system which increases reliability and longevity. Most load switches also allow for slew rate control and can provide protection under fault conditions.

Using an integrated load switch, such as ON Semiconductor’s NCP455xx series lets system designers access these benefits with a minimal increase in system component count. The high-performance devices provide a compact solution, occupying around 60% less PCB real estate versus a discrete solution.

Wide bandgap technologyPerhaps the most significant advance that will positively impact the size, reliability, efficiency and running costs of server power systems, is the move towards semiconductors based upon wide bandgap (WBG) materials such as gallium nitride (GaN) and silicon carbide (SiC). Designed to be inherently more efficient than silicon (Si) based devices, WBG devices are also able to operate at higher frequencies and higher temperatures.

As an example, in a 5kW boost converter of the type typically found in server power supply applications, replacing a Si switch with a SiC switch yields a 73% reduction in losses at frequencies around 80kHz, significantly improving system

Figure 3: SIC MOSFET advantages

efficiency. This contributes to a smaller system as less thermal management is required and also allows the system to run cooler, enhancing reliability and enabling greater component and system density.

While it is true that SiC MOSFETs remain more expensive than the equivalent IGBTs, the associated savings in passive components such as inductors and capacitors where values have dropped by 75% leads to an overall BOM cost that is lower for the SiC design, than for the Si design. Importantly and in addition, the energy cost savings yielded can total tens of thousands or even millions of dollars over the life of server installations.

SummaryThe need for huge and ever-increasing amounts of data storage is creating a very competitive landscape within the world of data centers. Real-estate space and electrical energy are two of the biggest costs and as operators seek to reduce these, they are demanding ever more efficient, reliable and smaller power solutions for the servers and storage devices.

While there are many aspects to consider when designing a successful server power solution, highly integrated devices such as integrated MOSFETS, SPS, eFuses and load management are enabling designers to create sophisticated power solutions

that are efficient, compact and reliable. E-fuses play a pivotal role in maintaining uptime as they facilitate hot swapping of devices that are prone to failure such as HDDs and fans.

Looking to the near future, WBG materials promise a step change in size and performance as well as improved reliability and efficiency that will reduce operational expenditure. Having now reached the point where the BOM cost for a WBG solution is comparable to, or lower than, a similar silicon design, the uptake of these devices is expected to accelerate.

On Semiconductorhttps://www.onsemi.com

www.taiyo-yuden.com

Telecommunication, Information, Consumer, Industry and Automotive Electronics

HIGHEND QUALITY ELECTRONIC COMPONENTS


Special Report:Automotive Electronics + Infotainment

Inside:

Implementing Fast DC BEV Chargers Up to 150 kW...

Electronic Pervasiveness in Vehicles Brings EMI Challenges...

Designing for a Safer Future...

Battery Monitor Maximizes Performance of Li-Ion Batteries in Hybrid & EV...

Improving Mild Hybrid EV Power Supply Systems with High Step-Down Ratio

DC/DC Converters...

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SPECIAL REPORT : AUTOMOTIVE ELECTRONICS + INFOTAINMENT



Implementing Fast DC BEV Chargers Up to 150 kW

By: Omar Harmon, Francesco Di Domenico and Srivatsa Raghunath, Infineon Technologies

If BEVs are to be useful for long-distance journeys, the charging infrastructure has to be closer to today’s experience of refuelling a petrol or diesel vehicle

One cannot fail to notice that our city streets and car parks are going through a

slow transformation: they are beck-oning the age of the electric ve-hicle. As the battery electric vehicle (BEV) grows in popularity, the in-frastructure to keep them charged is appearing to meet demand. While the majority of BEVs are yet to compete on range with internal combustion engine (ICE) vehicles, range-angst need not be an issue if BEVs could be recharged in a time frame approaching that of a typical filling station visit.

For home charging, most BEVs can be charged either from the domestic AC supply or via a wall-mounted charger. Rated typically at up to 22 kW, such solutions pro-vide enough charge for a further 200 km in around 120 minutes.

This is ideal for overnight refuel-ling. However, to achieve the same range in around 15 minutes (one-eighth of the time) would require a DC charger rated at 150 kW. Such power can only be delivered in dedicated locations where the nec-essary electrical infrastructure is in place, with service stations, taxi ranks and existing filling stations being ideal candidate locations.

Taking a modular approachRegional standards for chargers are already well established, with organisations such as CharIN in Europe, CHAdeMO in Japan, and GB/T in China having defined everything from connectors and cables to charging voltages and currents. Further standards are also applicable that cover general aspects of electrical safety (IEC 60950), optical isolation (UL1577) and magnetic and capacitive (VDE

V 0844-11) coupling components. This leaves developers the free-dom to choose how to best ap-proach the implementation of the DC charger.

Issues such as form factor, envi-ronment, aesthetics and price will influence many aspects of the de-sign. However, regardless of these requirements, DC chargers in the 50 kW to 150 kW range will require a modular approach. These are linked together via a data bus to a central control system that handles billing. Additionally, it undertakes authentication with external data networks and ensures that the authenticity of any replacement modules fitted to the charger.

To date, typical 50 kW chargers have been implemented by com-bining three separate hardware sub-units of around 16.5 kW each.

The sub-units, in turn, are imple-mented by combining three 5.5 kW design blocks within each of them. This modular approach makes it possible to achieve economies of scale for manufacturers, enabling them to reuse existing sub-units and design blocks when address-ing new customers. In the event of a failure, the modular approach also simplifies maintenance and repairs. With the push towards shorter charge times the power that must be delivered rises, result-ing in the power delivered by each sub-unit and design block rising to provide a balance between perfor-mance, power, and ease of use.

The sub-units themselves are based upon efficient multi-level, multi-phase topologies allow-ing heat generation to be spread across the available volume, as

well as enabling scalability. The modular approach also enables general economies of scale, en-abling manufactures to quickly implement a wide array of charger output powers as market demands develop.

Sub-unit topologies for 30 kWIn the 15 kW to 40 kW power range, a design approach using discrete components is recommended for sub-units. The goal is to achieve efficiencies of between 93 and 95 percent while supporting an output voltage range of 200 to 920 VDC (CharIN). The input supply, typi-cally 3-phase, 380 VAC, is rectified using a 3-phase Vienna Rectifier. From here, isolated DC/DC single full bridge resonant LLC converters (for 1200 V), or stacked full bridge LLCs (for 600 to 650 V), are used to deliver the variable DC output.

The design should be

As long as DC chargers are not required to feed energy back into the grid, the Vienna Rectifier makes an excellent choice for the PFC stage. This 3-phase, three level PWM rectifier requires only three active switches. Its output voltage can be controlled and it remains operational even in the event of un-balanced mains or the loss of one phase. It is also robust since, in the event of a malfunction of the con-trol circuit, there is no short circuit of the output or the front end. The input current is sinusoidal, with various implementations being shown to achieve a Power Factor of up to 0.997, THDs of below 5 per-cent, and efficiencies of 97 percent or better.

Such a topology is efficiently Figure 1: Typical topology for charging sub-unit in 15 – 40 kW range

Figure 2: Proposed design for a 30 kW charging sub-unit

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implemented with a combination of silicon and silicon carbide (SiC) technologies. Devices such as the CoolSiC 1200V 5th generation Schottky diodes deliver tempera-ture independent switching behav-iour, high dv/dt ruggedness and a low forward voltage of just 1.25 V. This reduces overall system cooling requirements and increases system reliability while offering extremely fast switching. For efficient and cost optimised solutions, the 650 V TRENCHSTOP 5 IGBTs, with their low VCEsat and switching losses, can be paired with these diodes. Alternatively, to achieve further efficiency improvements, they can be matched with the CoolMOS P7 series in the back-to-back switching stage. These provide a significant reduction in switching losses due to their low Eoss, improved gate charge (Qg), and low RDS(on) that

can be as low as 24 mΩ.

The two stacked resonant full bridge LLC converters make use of CoolMOS CFD7 devices featuring a fast body diode. This provides pro-tection during the critical operating phases of a BEV charger, specifi-cally during start-up, in the event of a short circuit at the output, or burst mode. This ruggedness is not provided at the expense of other characteristics, with the devices delivering low Eoss, Qg, and reverse recovery charge (Qrr). The granular RDS(on) provided across the fam-ily enables selection of a “best-fit” device for each power class. The secondary rectification stage is completed with 650 V CoolSiC™ Schottky diodes.

Attaining more efficiency for 30 kW sub-units

By moving to an implementation with a higher share of SiC devices, the same topology can be made more efficient. In addition, due to the lower number of components, reliability is increased while heat generation is reduced. The high-voltage DC/DC stacked approach is replaced with parallel full-bridge LLC converters. To accommodate the higher DC-link voltages on the primary side, the switches are replaced with 1200 V CoolSiC MOS-FETs. The higher secondary-side voltages are handled by upgrad-ing the diodes to 1200 V CoolSiC devices. The combination of fewer components, together with the low-er RDS(on) provided by each device, delivers lower conduction losses. Overall, sub-units taking this ap-proach deliver a longer lifetime with higher reliability, increased power density, and enable operation at

higher switching frequencies.

Selection of the optimal gate driverThe control signals from a mi-crocontroller (MCU), such as an XMC4000, or digital signal proces-sor (DSP) need to be linked to the power devices via a suitable gate driver. Solutions based upon sili-con-on-insulator (SOI) technology with monolithic level-shift robust-ness and galvanically isolated core-less transformer (CT) technology provide the required performance for driving both half and full-bride stages. Critical performance mea-surements include the propagation delay, drive current, VS immunity, level-shift losses, and switching frequency, to name but a few.

The designs discussed utilise two families of the EiceDRIVER range; the 1ED and 2EDi. Solutions such as the 1EDCx0I12AH are single channel isolated CT gate drivers offered in a wide body package and are certified to UL-1577. The input side supports a wide range of voltages, simplifying connec-tion to an MCU or DSP, as does the output side with support for both unipolar and bipolar opera-tion. The rail-to-rail output driver

Figure 3: Making the resonant full bridge LLC stage entirely from SiC components delivers further gains in system efficiency

simplifies gate resistor selection, saves on an external high-current bypass diode, and enhances dv/dt control in both high and low-side configurations.

The 2EDS8265H is a fast dual-channel gate driver, with isola-tion between both the input and output sides, as well as channel-to-channel isolation on the output side. The excellent common-mode rejection, fast signal propaga-tion, and high drive current is well suited to the CoolMOS CFD7 and CoolSiC devices used in the primary side of the stacked LLC.

In the context of a BEV fast char-ger features such as active shut-down, in situations where the output device is not connected to the power supply, and under volt-age lockout (UVLO) contribute to the robustness of the overall solution. In conjunction with an optimal layout, such as locating decoupling capacitors close to the input and output supply pins and reducing the parasitic inductance with ground planes, ensures good thermal and electrical (noise immunity) performance can be attained.

SummaryFor BEVs to become a mode of transport that are equally at home on long-distance journeys as they are for short, inner-city use, the charging infrastructure needs to move closer to today’s experience refuelling a petrol or diesel vehicle. For this, fast DC chargers delivering up to 150 kW are part of the solu-tion. Chargers of this dimension are taking a modular approach, com-bining several lower power units to achieve the desired output power.

With efficiency, reliability, thermal considerations, size and cost all un-der close scrutiny, it is clear that SiC devices will play an important role in developing the required solu-tions. These may be combined with existing silicon MOSFET switches or, where highest efficiencies need to be achieved along with a lower part count, in combination with SiC switches. Together with the ap-propriate gate drivers and control electronics, air-cooled 30 kW or greater modules can be realised to meet current worldwide charging standards.

Infineon technologieswww.infineon.com

Figure 4: Block diagrams for the single and dual-channel coreless transformer EiceDRIVER gate drivers

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Electronic Pervasiveness in Vehicles Brings EMI Challenges

By: Felix Corbett, TTI Europe

Investigating the suppression and filtering components that can be used to help ensure interoperability between systems within the modern car

The integration of more and more electronics

in cars is being driven by automotive industry trends such as the ‘connected car’, increased used of ADAS (advanced driver assistance systems), and the drive towards semi- or even fully autonomous vehicles. The potential for EMI/EMC issues is therefore dramatically increasing with this growing pervasiveness of electronic systems and their physical proximity within the car. In addition, EMI will be an even greater issue in electrically powered vehicles that rely on high-current systems in the automotive drivetrain with the potential for significant transients.

Today’s modern car has more than a hundred processors running systems from critical drive-by-wire functionality to body electronics such as electric

mirrors or door locks to in-car functionality such as mood lighting, heated seats or the infotainment system. This latter machinery introduces a host of communications signals coming in from external sources including GPS, radio broadcasts, cellular internet connectivity and data streaming via Wi-Fi or Bluetooth from mobile phones (figure 1). In addition, other signals are introduced

from safety systems such as collision-avoidance radar or tyre-pressure monitoring, which is typically uses RF communication. All these create potential EMI problems and therefore signal interference protection is required for drive-by-wire functionality, or systems such as ADAS, which can make potentially life-changing decisions, or other safety devices. For example, there have

been a host of reported incidents concerning the triggering of airbags by RF transmissions.

But this is not all: new technologies are being introduced in the coming years, such as the ‘Internet of Moving Things’ (IoMT). This will include Car-to-Car (C2C) and Car-to-Infrastructure (C2I) communication, providing a view of traffic conditions and potential hazards. These two technical initiatives will use IEEE802.11p, an automotive-specific version of Wi-Fi. Additionally, inside the vehicle, data is transferred via a wide range of buses and protocols, including: CAN (Controller Area Network) for routine functions; the MOST (Media Oriented Systems Transport) protocol for multimedia; and FlexRay for critical controls such as braking and steering. Ethernet cabling is being used to transport these communications, but commonly two-wire unshielded cable is employed as it offers significant savings in weight compared to shielded multi-conductor cables.

ElectricThe use of high-power motors and drives in electric vehicles will bring a further range of challenges. The battery’s DC bus is switched at high frequency to generate AC for traction motors; and switched-mode converters down-convert the bus voltage to 12 or 24V for ancillary equipment and the remainder of the electronics (Figure 1).

IGBTs will typically perform the DC switching at relatively low frequency to maintain efficiency. However, Silicon Carbide (SiC) based devices are increasingly being used and these can operate at much higher frequencies with good efficiency. This means a reduction in size of passive components such as magnetics and capacitors, thereby reducing cost and weight. But there is a penalty in terms of EMI, especially at higher frequencies.

TypesEMI falls into distinct categories – emissions and immunity – both conducted and radiated. Emissions need to be considered concerning their effect on internal systems, other vehicles and the immediate environment in general; and conducted EMI can come from outside via charging stations, as well as from internal systems. Radiated EMI can originate from a car’s own communication systems, as well as externally from other vehicles or from high-power sources such as broadcast transmitters.

Conducted interference, in the form of extraneous communication signals or noise, can be split further into ‘common mode’ (CM) and ‘differential mode’ (DM). DM interference is between connections and their intended current return path. CM interference appears on electrical connections with respect to the local ground or chassis and can be difficult to identify and control (Figure 2).

In addition, increasing use of plastic and carbon-fibre panels means that the classic metal chassis cannot be guaranteed as a screening ‘cage’ or even as a low impedance overall ground.

MitigationDesigning-in good EMC performance is an obvious point and simulation tools can help in this process. But as well as demanding a high level of emissions and susceptibility performance from components and modules, it is also important to consider interconnections, grounding and shielding and, naturally, compromises will be required in terms of cost and weight.

The problem becomes greater with the high currents involved in electric vehicles. Use of the metal chassis as a return is cheaper and lighter than having a dedicated cable, but almost certainly will not deliver the same level of EMI performance. However, edge rates of switching power

Figure 1: Electric vehicle powertrain (source – US DoE)

Figure 2: Common-mode and differential-mode noise currents (source TTI)

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converters can be controlled to minimise the spectrum of emissions, and topologies can be chosen that naturally have lower emissions without an efficiency penalty. For example, resonant conversion techniques are increasingly common, but at the expense of complexity. But taking a holistic approach, any extra expense can be offset by savings in filtering elsewhere.

Filters to slow data edges can be employed along with balanced-pair data cabling for

minimum radiation and pick-up. Although screens can effectively protect signals, they can also provide unwanted return paths for power or other signals without careful termination. Differential and common-mode chokes in signal and power lines can be helpful, but they will also require capacitors to shunt away interference.

If EMI is just blocked with the high impedance of an inductive filter, it generates a voltage which can then be coupled elsewhere as interference. Filters can also interact to produce unwanted resonances and voltage peaking, so these need to be designed carefully with appropriate damping and controlled input/output impedances.

Transient limiters are also useful in the form of varistors, clamp zeners or simply diodes on inputs to clamp the signals to the rail voltages as a maximum. However, varistors are low cost and have a wear-out mechanism with stress, so cannot deliver reliable performance over long periods.

At the subsystem level, modules will have been evaluated for their EMC performance on an individual basis, but they

will produce quite different performances with real-life I/O, which is why holistic testing is vital. Overall, there are an almost infinite number of permutations of interference types, levels and effects, so FMEA (Failure Mode and Effect Analysis) will be necessary to mitigate the effects with a hierarchy of fail-safe mechanisms.

SuppressionComponents intended for automotive will be rated for harsh temperatures and for thermal shock and high vibration. Employed in the Murata GCJ, GCG and GCB series of multilayer capacitors, for example, techniques are used to ‘proof’ component terminations against mechanical stress such as ‘soft’ electrodes or even conductive glue. Additionally, high-reliability types may offer a special construction, so that a stress-induced internal electrode short circuit means reduced capacitance rather than causing a total end-to-end short.

Inductors can have the same protection mechanisms. Surface-mount inductors and dual-winding /common mode chokes will often be based on ceramic core technology, offering stability and high-temperature performance, such as those from Bourns and TDK Electronics. TTI Europe

https://www.ttieurope.com/content/ttieurope/en.html

Figure 3: Edge rates of power converters in the nanosecond range (source TTI)

Figure 4: Filters may need damping to avoid instability (source TTI)

Designing for a Safer Future

By: Mike Branch, Vice President Data & Analytics, Geotab

Connected cars and the IoT technologies driving society beyond mobility

Since the introduction of the mechanical assem-bly line by Henry Ford more than a century

ago, vehicles and technology have shared a long and inextricable his-tory of automation, with continu-ous innovation not only central to the evolution of automobile design but also essential to advancing the smart city revolution taking place across the globe. With a sharp focus on improving urban mobility, increasing safety and reducing pol-lution, pioneering public, private and government organizations are turning to Internet of Things (IoT) technologies—and connected ve-hicles—to tackle some of the most challenging issues facing society. Though connected cars are not yet ubiquitous, most vehicles today are equipped with some wireless capability. While newer and recent-year vehicles are shipped with an embedded, factory-installed con-nected vehicle system, even older vehicles typically have the ability to connect via a self-contained aftermarket software and hardware telematics device that is easily installed into a vehicle's OBDII (on-board diagnostics) port. Mov-ing forward, however, connectivity will only increase. In its inaugural connected vehicle forecast, Inter-national Data Corporation (IDC) examined the global and U.S.

connected vehicle market for the 2018–2023 period and estimated that, by 2023, nearly 70 percent of worldwide new light-duty vehicles and trucks will be shipped with embedded connectivity. In the U.S., IDC expects nearly 90 percent of new vehicles shipped to include embedded connectivity by 2023.

Vehicles Connecting to InfrastructureAn IoT communication system, Vehicle-to-Infrastructure (V2I) is one of several connected car tech-nologies enabling new solutions to improve the way we live, work and commute. Consider Washington D.C., which is ranked by INRIX ahead of Los Angeles and New York City for traffic congestion.

With less than 1 million residents, it has one of the highest ratios of traffic signals per square mile at 26.06 (LA has only 8.78), result-ing in constant gridlock. Using V2I communications systems, the Dis-trict Department of Transportation (DDOT) aims to advance its mis-sion to “enhance the quality of life for District residents and visitors by ensuring that people, goods and information move efficiently and safely, with minimal adverse impact on residents and the envi-ronment.” Enabling the sharing of data between connected vehicles and sensors embedded in critical elements of a city’s infrastruc-ture—traffic lights, lane markers, streetlights, signage and parking meters among other things—V2I

Figure 1: The GO9 device allows you to lead your fleet into the future with expanded capacity for further native vehicle support, improved fuel usage support, electric vehicles and global expansion. Geotab’s technology transforms big data into Smart Data to create Smart ecosystems, which turn into Smart Cities.





Trial V2X projects are well under-way across America in places such as Las Vegas, Utah and Geor-gia, where a pilot program was launched halfway between Atlanta and Montgomery, Alabama, along an 18-mile stretch of Interstate 85 known as The Ray, named after industrial sustainability champion Ray C. Anderson. According to technology partner Panasonic, the section serves as a “living laboratory for technologies that make driving safer, smarter and more sustainable” and a “prov-ing ground for reinventing what a highway could and should be.”

Connected car data communicating through a central telematics hubCentral to V2X connectivity, telematics provides a central hub for all connected car data. Though the technology has been avail-able for decades, the latest in-

cab systems are state of the art and designed to rapidly collect and transfer consistent telemetry data via V2V and V2I engagement. Today, telematics systems are be-ing deployed for a wide range of initiatives in municipalities and states across the U.S. In Septem-ber 2019, the State of Colorado’s Division of Capital Assets (DCA) announced plans to roll out a fully integrated Electric Vehicle (EV) fleet management solution to accelerate Colorado’s transition to clean energy and support the State’s Electric Vehicle Plan. Equip-ping government vehicles with a cutting-edge telematics platform that tracks and measures fleet efficiency, as well as conventional fuel and electricity consumption, the DCA will ensure more reliable, environmentally responsible and cost-effective fleets as the state works toward combating climate change, reducing pollution and

modernizing grid infrastructure. The State of California also imple-mented a telematics solution as part of its goal to promote reli-able, environmentally responsible and cost-effective state, municipal and county fleet while supporting several green initiatives targeted at improving fleet operations and reducing harmful environmental impact. By giving regional govern-ments unprecedented access to a leading-edge computing and analytics platform, these states and others will have the ability to put connected-vehicle data to use within a myriad of smart city and smart state initiatives. In the same way the audacious idea of replacing the Ameri-can horse and buggy with the Model T evolved beyond what Henry Ford likely imagined, future generations of connected vehicles will inevitably be de-signed to do far more for than transport people from one place to another. Embedded with IoT technologies, these “sensors on wheels,” with real-time data sharing at the core, could collect and process helpful informa-tion to improve every aspect of society. As a result, traffic jams, accidents, mobility challenges and perhaps pollution will one day become a thing of the past. In the meantime, we collectively have a shared responsibility and an opportunity to find solutions that drive civilization forward.

Geotab, Inc.https://www.geotab.com/

Figure 3: MyGeotab is a web-based fleet management software that reports fuel usage and consumption, driver safety, road & safety risks and needed vehicle maintenance

is empowering decision makers and drivers with real-time infor-mation that has the potential to relieve congestion while advancing the District’s goal to reduce traffic-related deaths to zero. Equipped with cameras and sensors, smart traffic lights, for example, can detect whether one or many cars are waiting in specific lanes. Us-ing this information, calculations are quickly run to determine the amount of time it will take to clear lanes. Smart signals can also com-municate with other nearby smart signals or connect to the grid as a network of signals, working in tandem to improve traffic flow. These signals can also respond intelligently to data received from connected vehicles and mobility apps to warn drivers that they are about to drive through a red light or sense when a pedestrian is ar-riving and activate the crosswalk. V2I technology is also designed to improve the parking experience, with connected parking spaces communicating to the vehicle which spots are available. This technology reduces parking frus-tration for vehicle owners while simplifying occupancy tracking and beyond for parking lot attendants.

Vehicles Connecting to VehiclesVehicle-to-Vehicle (V2V) is another significant connected car technolo-gy shaping the future of intelligent transportation and smart cities. Current cutting-edge ultrasonic, ra-dar and camera technologies that allow a vehicle to see and analyze its surroundings and make safe decisions while driving rely mostly

on sensors, which have limited range. When it comes to hidden objects and unexpected behavior from other vehicles, these systems run into the same problems as humans do—although they react much quicker. V2V communica-tions systems can correct this weakness by letting cars speak with one another directly and share information about their position, speed and status. With intersec-tion movement assist (IMA), left turn assist (LTA) and the ability to see farther and enhance the level of predictability, V2V technologies are expected to have a big impact on road safety.

Vehicles connecting to everything

Vehicle-to-Everything communica-tions, or V2X, combines V2I, V2V, V2P (vehicle-to-pedestrian) and V2N (vehicle-to-network, which connects to cellular infrastructure and the cloud) and extends those benefits to others on the roadway. With Wi-Fi and 5G serving as the backbone, V2X enhances auto-mation with capabilities that will further improve safety and trans-portation infrastructure. Functions include:

• Informing autonomous ve-hicles of out-of-sight vehicles

• Warning distracted pedestri-ans of oncoming traffic

• Delivering alerts for weather and road conditions to drivers

Figure 2: Heatmap depicting temperature in New York city via sensor network over the course of one day – Geotab’s solutions capture 30 billion data points per day across the world.



Battery Monitor Maximizes Performance of Li-Ion Batteries in Hybrid & EV

By: Cosimo Carriero, Analog Devices, Inc.

Lithium-ion (Li-Ion) batteries are a popular way to store energy in electric and hybrid vehicles as they offer the highest energy density of any current battery technology

To maximize perfor-mance with li-ion batter-ies, a battery monitoring system (BMS) is man-

datory. BMS not only allows you to extract the highest quantity of charge from your battery pack, but also lets you manage the charge and discharge cycles in a safer way, which results in an extended life.

Accurately measuring a battery’s state of charge (SOC) increases battery run time or decreases weight. A precise and stable device does not require factory calibra-tion after PCB assembly. Stability over time improves safety and avoids warranty problems. A self-diagnostics feature helps reach the right automotive safety integ-rity level (ASIL). A battery pack is a challenging environment for electromagnetic interferences (EMI), so special care has been put into designing the data communication link to ensure robust and reliable communication between the measurement chips and the system controller. Cables

and connectors are among the main causes of failures in battery systems, so wireless solutions should be considered.

IntroductionAn energy storage unit has to pro-vide high capacity and the ability to release energy in a controlled

manner. Storage and release of energy, if not properly controlled, can result in a failure of the battery and ultimately fire. Battery failure can come from mechanical stress or damage, electrical overstress in the forms of deep discharge, over-charging, overcurrent, and thermal overstress. To reach the highest

levels of efficiency and safety, a battery monitoring system is required.

The main function of the BMS is to keep any single cell of the battery pack inside its safe operating area (SOA) by monitoring the following physical quantities: stack charge and discharge cur-rent, single cell voltage, and battery pack temperature. Based on these quantities, not only can the battery be operated safely, but also SOC and state of health (SOH) can be computed.

Another important feature provid-ed by the BMS is cell balancing. In a battery stack, single cells can be arranged in parallel and in series to achieve the required capacity and operating voltage (up to 1 kV or higher). Accurate cell balancing is a significant feature in a BMS, enabling safe operation of a bat-tery system at its highest capacity.

BMS ArchitecturesAn electric vehicle battery consists of several cells stacked in series. A typical stack—with 96 cells in series—when charged at 4.2 V can develop a total voltage in excess of 400 V. Higher voltages can be reached by stacking more cells. Charge and discharge current are the same for all the cells, but voltages have to be monitored on every single cell. To accommodate the cells required for high powered automotive systems, batteries are

often divided into modules, and distributed throughout available spaces in the vehicle. A modular design can be used as the basis for very large battery stacks. It allows battery packs to be distributed over larger areas for more effective use of space.

Analog Devices has developed a family of battery monitors ca-pable of measuring up to 18 series connected cells. The AD7284 can measure 8 cells, the LTC6811 can

Figure 1: A 96 cell battery pack architecture with the 12-channel LTC6811 measurement IC.

Figure 3: Series modules with CAN gateway.

Figure 2: Parallel independent CAN modules.



measure 12 cells, and the LTC6813 can measure 18 cells.

To support a distributed, modular topology within the high EMI environment of an EV/HEV, a robust communication system is required. Both isolated CAN bus and ADI’s isoSPI™ offer road-proven solutions for interconnecting modules in this environment.1 While the CAN bus provides a well-established network for interconnecting battery modules in automotive applications, it requires a number of additional components. The primary downside of a CAN bus is the added cost and board space required for these additional elements. Figure 2 shows a possible architecture based on

CAN. In this case, all modules are parallel connected.

An alternative to a CAN bus in-terface is ADI’s innovative 2-wire isoSPI interface.1 Integrated into every LTC6811, the isoSPI interface uses a simple transformer and a single twisted pair, as opposed to the four wires required by the CAN bus. Figure 3 shows the architec-ture based on isoSPI and using a CAN module as a gateway.

There are pros and cons to the two architectures presented. CAN modules are standard and can be operated with other CAN subsys-tems sharing the same bus; the isoSPI interface is proprietary and communication can happen only with devices of the same type. On

the other hand, the isoSPI mod-ules do not require an additional transceiver and the MCU to handle the software stack, resulting in a more compact and easy-to-use so-lution. Both architectures require a wired connection, which has disad-vantages in a modern BMS, where routing wires to disparate modules can be an intractable problem, while adding significant weight and complexity. Wires are also prone to pick up noise, leading to the requirement for additional filtering.

Wireless BMSWireless BMS removes the com-munication wiring.1 In a wireless BMS, each module is intercon-nected via a wireless connection. The biggest advantages of a wire-less connection for large multicell

battery stacks are:

• Reduced wiring complexity• Less weight• Lower cost• Improved safety and reliability

Wireless communication is a challenge due to the harsh EMI environment, and the RF shielding metal posing as obstacles to signal propagation.

ADI’s SmartMesh® embedded wireless network, field-proven in industrial Internet of Things (IoT)

applications, delivers >99.999% reliable connectivity in industrial, automotive, and other harsh en-vironments by employing redun-dancy through path and frequency diversity.

The Importance of an Accurate MeasurementAccuracy is an important feature for a BMS and is critical for LiFe-PO4 batteries.3,4 Let’s consider the example in Figure 5. To prevent overcharge and discharge, the cells of the battery are kept between 10% and 90% of full capacity. In a

Figure 4: Battery monitoring interconnections comparison

Figure 5: Battery charge limits

Figure 6: LTC6811 measurement error vs. temperature

85 kWh battery, only 67.4 kWh are available for normal driving. If there is a measurement error of 5%, to continue to op-erate the battery safely, the cells must be kept between 15% and 85% of their capacity. The total available capacity has been reduced from 80% to 70%. If accuracy is improved to 1%, the battery can be operated

now between 11% and 89% of full capacity, with a gain of 8%. With the same battery and a more ac-curate BMS, automobile mileage per charge is increased.

Circuit designers rely on data sheet specifications to estimate the accu-racy of a cell measurement circuit. Other real-world effects often dominate the measurement error. Factors affecting the measurement accuracy include:

• Initial tolerance• Temperature drift• Long-term drift• Humidity• PCB assembly stress• Noise rejection

A good technology must consider these factors to deliver very high performance. Measurement ac-curacy of the IC is primarily limited by the voltage reference, which is sensitive to the mechanical stress. Thermal cycling during PCB sol-dering stresses silicon. Humidity is another cause of silicon stress as water is absorbed in the pack-



age. Silicon stress relaxes over time, leading to long term drift of the voltage reference.

Battery measurement ICs use either a band gap voltage reference or a Zener voltage reference. IC design-ers use an NPN emitter-base junc-tion operating in reverse breakdown as a Zener reference. Breakdown occurs at the surface of the die. These junctions are noisy and suffer

from unpredictable short- and long-term drift. The buried Zener places the junction below the surface of the silicon, well away from contami-nation and oxide effects. The result is a Zener with excellent long-term stability, low noise, and relatively accurate initial tolerance.

The LTC68xx family uses a labora-tory grade Zener reference. Figure 6 shows the drift over temperature of

the battery measurement IC error for five typical units.

Figure 7 shows a comparison of the long-term drift for a bandgap volt-age reference IC and a buried Zener voltage reference IC. The picture clearly shows a much better stabil-ity of the Zener reference over time, at least 5× better than bandgap reference. Similar tests for humidity and PCB assembly stress show the superior performance of the buried Zener over the band gap voltage reference.

Another limiting factor for accu-racy is noise. A car battery is a very harsh environment for electronics due to the electromagnetic inter-ference generated by the electric motor, the power inverter, the dc-to-dc converters, and other high current switching systems in an EV/HEV. The BMS should provide a high level of noise rejection in order to maintain accuracy. Due to the high number of cell voltages to be converted and transmitted, the con-version time can’t be too slow. SAR converters might be the preferred choice, but in a multiplexed system, speed is limited by the settling time of the multiplexed signal. In this case, sigma-delta (Σ-Δ) converters can be a valid alternative.

ADI measurement ICs use sigma-delta analog-to-digital converters (ADCs). With a sigma-delta con-verter, the input is sampled many times during a conversion, and then averaged. The LTC6811 uses a third-order sigma-delta ADC with programmable sample rates and

Figure 7: Long-term drift comparison between buried Zener diode and bandgap voltage references.

Figure 9: A 12-cell battery stack module with active balancing.

Figure 8: ADC filter programmable ranges and frequency response.

eight selectable cutoff frequencies. Figure 8 shows the filter response for the eight programmable cutoff frequencies..

Cell Balancing for Optimized Battery CapacityBattery cells, even if accurately manufactured and selected, show slight differences from each other. Any mismatch in capacity between the cells results in a reduction of the overall pack capacity.

Let’s consider our example where the cells were kept between 10% and 90% of the full capacity. The effective lifetime of a battery can be significantly shortened by deep

discharge or overcharging. There-fore, the BMS provides undervolt-age protection (UVP) and overvolt-age protection (OVP) circuitry to help prevent these conditions. The charging process is stopped when the lowest capacity cell reaches the OVP threshold. In this case, the other cells are not fully charged and the battery is not storing the maxi-mum allowed energy. Similarly, the system is stopped when the low-est charged cell hits the UVP limit. Also, there is still energy in the bat-tery to power the system, but, for safety reasons, it can’t be used.It is clear that the weakest cell in the stack dominates the performances of the full battery. Cell balancing is a

technique that helps overcome this issue by equalizing the voltage and SOC among the cells when they are at full charge.5 There are two tech-niques for cell balancing—passive and active.

With passive balancing, if one cell becomes overcharged, the excess charge is dissipated into a resistor. Typically, there is a shunt circuit which consists of a resistor and a power MOSFET used as a switch. When the cell is overcharged the MOSFET is closed and the excess energy is dissipated into the resistor. Active balancing, on the other hand, redistributes the excess energy between the other cells of the module. This way the energy is recovered and less heat is generated.

ConclusionElectrification is key for lower emission vehicles, yet requires a smart management of the energy source—the Li-Ion battery. If not managed properly, a battery pack can become unreliable, and drastically reduce the safety of the automobile. High accuracy helps maximize the performance and the life of the battery. Active and passive cell balancing allow a safe and efficient battery management. Distributed battery modules are easily supported, and a robust communication of the data to the BMS controller, both wired and wireless, allows reliable SOC and SOH calculations.

Analog Deviceswww.analog.com



Improving Mild Hybrid EV Power Supply Systems with High Step-Down Ratio DC/DC Converters

By: Satya Dixit, Sr. Director of Solution Mktg & App, ROHM Semiconductor

The need to combat global warming has prompted many countries to establish vehicle emission mandates, with the most severe restrictions enacted in Europe

To achieve the regulatory limits set by a number of countries worldwide, automakers

are increasingly working on developing electric vehicles.

Currently, 5 types of electric vehicle technologies are being employed: Pure EV, powered solely by electricity, Fuel Cell EV

that runs on fuel cells, Strong Hybrid, which charges using regenerative energy and supports electric-only operation, Plug-In Hybrids that can be charged with a standard AC outlet, and Mild Hybrid that adds a 48V li-ion battery to conventional 12V vehicle systems to supply more power to the hybrid motor and support heavier load

components while still improving fuel efficiency.

How does the shift towards electric motors improve fuel economy? In the case of conventional vehicles with gasoline-powered engines, a lead-acid battery charged by the alternator powers all electrical systems, including

lighting and AC. Consequently, fuel efficiency decreases as the electrical systems are used, whereas in electric-powered vehicles regenerative energy (i.e. generated through braking) charges a lithium-ion battery that powers the electrical systems. This reduces the amount of engine power used, improving fuel economy.

Strong Hybrid and Plug-In Hybrid systems are extremely effective in reducing CO2 emissions, but they entail significant additional costs and are difficult to install in compact vehicles. As a result, 48V Mild Hybrid systems that provide a lower-priced solution while still reducing CO2 emission compared with conventional 12V vehicles are attracting increased attention. In fact, according to IHS, roughly 50% of the hybrid market, or 1 out of 10 vehicles sold worldwide, will be a 48V Mild Hybrid.

Power Supply ICs for Mild Hybrid EVsThe main difference between Mild Hybrid and standard vehicles is

the power supply voltage of the battery. Mild Hybrid systems utilize a 48V battery, 4x the voltage of internal combustion (IC) systems (12V). And because all other elements remain the same (including ECUs), the input/output voltage difference is significantly increased.

Consequently, DC/DC converters with high step-down ratio capable of generating a low output voltage from a much higher input voltage are required. Furthermore, to prevent radio interference in vehicle-mounted power supply ICs, a switching frequency of 2MHz is needed to ensure that the AM radio band (0.5MHz to 1.7MHz) is not affected.

Until now, it was common to use 2 chips for stepping the voltage down from 48V to the 3.3V or 5V demanded by ECUs (48V→12V→3.3V/5V). However, this doubles the number of peripheral components, increasing mounting area significantly. There is a way to use just one chip by lowering the

frequency to convert voltage, but this method requires larger coils and capacitors that generate harmonics which can interfere with the AM radio band.

For these reasons, there is an increasing demand for DC/DC converters capable of directly stepping down 48V input to 3.3V or 5V output at a switching frequency higher than the AM radio band. But to achieve this a number of obstacles must first be overcome.

Monolithic Power Supply IC Featuring Ultra-Narrow Pulse WidthOne technical hurdle for achieving lower output voltage from a higher input voltage at high frequency is narrowing the switching pulse width. The switching pulse width of a DC/DC converter is a function of the input voltage, output voltage, and switching frequency, and is calculated using the following formula:

(ton: Switching Pulse Width, VOUT: Output Voltage, VIN: Input Voltage, f: Switching Frequency)

As can be seen from the above equation, the switching pulse width narrows as the input voltage increases, output voltage decreases, and/or frequency rises. Therefore, a method for reducing the switching pulse width is required for 48V Mild Figure 1: Relationship between Duty Cycle and Output Voltage

Figure 2: Noise Components Increase at Higher Voltages and Frequencies



Hybrid systems. But to reduce pulse width it is first necessary to solve problems related to noise generation during switching.

Increasing the input voltage will cause the noise component to increase during switching due to parasitic inductance contained in the IC. The noise component will also rise at high frequencies, resulting from the higher switching frequency and parasitic capacitance of the element (Figure 2).

When this switching noise is introduced into the IC unstable operation may occur. To prevent this, conventional control methods utilize mask time. An analog circuit is also required for operation, which introduces a delay time. These two factors that arise due to the increased noise component cause the pulse width to become wider. Therefore, analog control is needed that leverages high voltage processes along with ultra-fast pulse control circuitry to detect information

before noise is generated and perform appropriate control.

The pulse width required to output 3.3V from 60V (the maximum voltage needed for 48V power supplies) is 30ns, but when considering load and power supply fluctuations within the IC a narrower pulse width is necessary. Ideally, the pulse width should be less than 20ns to achieve a step-down ratio of 24:1 (Figure 3). This will make it possible to provide stable 2.5V output from an input voltage range of 16V to 60V at a high frequency of 2MHz or more.

Adopting this technology will allow users to configure DC/DC converters capable of stepping down 48V to 3.3V using a single chip, instead of conventional systems that require 2 chips to first convert 48V to an intermediate voltage such as 12V, then from 12V to 3.3V.

At the same time, care needs to be taken to prevent IC destruction

Figure 3: Achieving Direct Step-Down from 60V to 2.5V at 2.1MHz

in the event of abnormalities. For example, when converting high input voltages to low output voltages, if the output and switching terminals are shorted a large amount of energy will be generated, causing large current flow which can lead to destruction in ICs employing conventional short-circuit detection methods. Therefore, a new type of protection technology is required for detecting abnormalities beforehand to protect the IC against large currents. Also, adopting a wettable flank package that provides superior wettability and visibility can contribute to improved mounting reliability for xEV applications.

ConclusionReducing CO2 emissions in vehicles is a major challenge and improving fuel efficiency an important step in achieving this goal. To this end, 48V mild hybrid vehicles that provide good cost performance is expected to see increased production – to the tune of 14 million vehicles by 2025 (a ninefold increase over current levels).

ROHM offers optimized solutions utilizing proprietary Nano Pulse technology that can lead to smaller, simpler power supplies in mild hybrid systems by providing considerable advantages over existing products.

ROHM Semiconductorwww.rohm.com


Since January 2004


POWER SYSTEMS DESIGNFINALthought

By: Ally Winning, European Editor, PSD

When Less is More

Balancing performance, size

and cost is always a chal-

lenge for designers of any

electronic component. For

power products it is no different. As

end products get smaller, the de-

mands on designers of power circuits

get tougher and tougher. Designs have

to fit into miniscule spaces, while still

being hyper efficient and costing very

little. It’s a barely possible task that of-

ten requires creating a completely new

power design for every new product.

Manufacturers of power components

are trying to keep up by offering small-

er and more efficient modules that will

assist designers, but that can come

at a cost – both from using the lat-

est technology and making so many

product variants that getting the full

benefits of large scale manufacturing

is not really possible. The speed of

innovation is not slowing, and new,

complex challenges have emerged in

datacentres, wearables, lighting and

automotive applications that leave

power component manufacturers

struggling to provide solutions for

every scenario.

One company stepped back to see

if there was a different way to tackle

the challenges that were emerging.

From that process, Vicor decided

to make fundamental changes to

the way that the company operates.

Firstly, it looked at the whole power

distribution network and developed

an overarching strategy for product

design. The strategy is based on us-

ing a 48V middle step between the

input voltage and point-of-load for

the greatest efficiency – no matter if

that voltage is from the mains or 12V

DC. The modules themselves would

use a single conversion topology that

Vicor has worked on over the last four

years. It is based on the company’s

0V/0I soft-switching for efficient

conversion that minimises losses.

Those conversion elements are then

combined on a panel depending on

voltage requirements of the final

module. The panels are then set in a

3D package with supporting compo-

nents for more efficient cooling. The

company already uses this technique

in its latest products to give what it

claims is the industry-leading power

density of 610W/cm3. By standardis-

ing on this single element, Vicor can

use the same production lines for any

product, getting greater economies of

scale and keep costs down.

The resulting products will provide

power designers with small modules

that are highly efficient and very cost-

effective. Because they combine the

three desired traits of efficiency, size

and cost, designers won’t be forced

to compromise, and fewer product

variations will be required. This, in

turn, will further decrease engineering

costs and allow power designs to be

easily repurposed for other products.

Vicor is so confident in its new strat-

egy that it has implemented a target

of tripling the company’s revenue,

and is making major investments to

significantly increase its manufactur-

ing capacity. Those plans include an

85,000 square foot extension at its

current manufacturing facility that is

due to be completed in the third quar-

ter of next year. It is a bold strategy

that attempts to reverse the trend of

more and more product variations.

The future will tell if it is the right one.

PSD


The Premier Global Event in Power ElectronicsTM

2020

New OrleansMARCH 15-19, 2020

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Special Report: Automotive Electronics + Infotainment

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