Compilation of Dis-/Advantages of DC-DC Conversion Schemes Power Task Force Meeting December 16 th,...

Compilation of Dis-/Advantagesof DC-DC Conversion Schemes

Power Task Force MeetingDecember 16th, 2008

Katja Klein1. Physikalisches Institut BRWTH Aachen University

Advantages: Grounding

Katja Klein 2Discussion of DC-DC Conversion

• Standard grounding scheme Module ground potentials are all the same Common ground reference for bias, analogue and digital voltage for whole substructure (rod, petal) Bias voltage ground reference is the same for all modules Easier for slow controls (difficult in SP to sense voltages)

Advantages: Communication


• Readout and control scheme is very standard AC-coupling of communication not needed Control chips can be supplied independently of modules

Advantages: Start-Up & Selective Powering


• Easy start-up Control chips can be powered on first If one converter per module, single modules can be powered on/off In scenario w/ charge pump per chip, single chips can be powered on/off

Advantages: Different Voltages


• Different voltages can be provided Buck-type converters: the same converter chip can be configured for different output voltages

Via a resistive bridge Two conversion steps can be combined No efficiency loss (in contrast to linear regulation in SP)

Can cope with Vopto > Vchip

Can cope with Vana ≠ Vdig

Charge pumps: only integer conversion ratios, defined by configuration

Advantages: Flexibility


• Great flexibility with respect to combination of modules with different load

Different numbers of readout chips Trigger modules vs. standard modules

power groups with different number of modules TEC vs. barrel

• In contrast, with SP current is fixed to highest current needed by any chain member chains must be uniform to avoid burning power in regulators

Advantages: Changing Loads


• Compatibility with changing loads, relevant for pixel detector

load is driven by occupancy trigger modules

• SP: the highest current potentially needed must always be provided inefficiency

Disadvantages: Chip Technology


• Need for a “high voltage“ tolerant process (10-12V) Good candidate identified, radiation hardness still to be proven Strong dependency on foundry: support of process over years? Any changes in process must be followed closely and irradiation tests be repeated

Disadvantages: Converter Efficiency


• Converter efficiency will be around 80% (ESR of passive components, Ron of transistors, switching losses)

Local generation of heat cooling of DC-DC converters needed Local efficiency decreases with lower conversion factor (Uout/Uin) Local efficiency decreases with higher switching frequency In two-step schemes efficiencies multiply

Disadvantages: Currents in Cables


• Cannot compete with Serial Powering Currents in power group with DC-DC conversion = I0nr

I0 = current of a single module n = number of parallely powered modules in the power group r = conversion ratio = Uout/Uin

Current in Serial Powering chain = I0, independent of n E.g. for 20 modules in power group need r = 20 to compensate Higher efficiency in SP (at least up to FE) less cooling needed Cables inside tracker volume can be thinner with SP

Disadvantages: Risks


• We have to stick with parallel powering Multiplicity (modules per cable) as today or higher Open connections (e.g. at PP1, PP0) lead to loss of power group Short on module leads to loss of power group

Protection needed? Use DC-DC converter to switch off module? Converter can break: can imagine isolated failures (loss of regulation...) and failures that lead to loss of power group (short) More risky if one converter powers several modules Do we need redundancy?

This adds mass

Disadvantages: Material & Space


• Material budget and space considerations Amount of copper in cables scales with current = I0nr

I0 = current of a single module n = number of modules in the power group r = conversion ratio = Uout/Uin

Air-core inductor (even if integrated into PCB, it needs a lot of copper) Filter capacitors, maybe other filter components With regulation (buck etc.), PCB traces can be narrow Without regulation (charge pumps), input voltage must be exact

Linear regulator or rather solid input traces Is shielding needed? How to design good low mass shielding?

Disadvantages: Material Budget


Simulated components: Kapton substrate with 4 copper layers Copper wire toroid Resistors & capacitors Chip

FE-hybrids

Kapton circuits

Analog Opto-Hybrids

Mother-boards

TEC1 converter / module

Disadvantages: Material Budget


Strip tracker

Total gain for strip tracker with 1 converter per module and a conversion ratio of 8; with power cables and motherboards modified accordingly:

Disadvantages: Noise


• DC-DC converters are undoubtedly noise sources (by design) Conductive noise through cables

Ripple on output voltage: switching frequency (1-5MHz) + higher harmonics are in the bandpath of the amplifier Switching leads to high frequency noise (tens of MHz, not so critical) Both CM and DM contributions

Radiated noise From inductor near field via inductive (and capacitive?) coupling From cables

Has to be taken into account for all aspects of electronics system design: readout chip, FE-hybrid, grounding & shielding, motherboard, layout ... Not clear what to prepare for: noise depends on implementation

For same chip, noise emission can be rather different depending on PCB etc. Scalability from lab system to complete detector not obvious PS noise requirements to be understood

Compilation of Dis-/Advantages of DC-DC Conversion Schemes Power Task Force Meeting December 16 th,...

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