Considerations When Designing with Isolation and Isolated Driver Devices

Kevin HuangTom Gao

2

What is Isolation?

♦Galvanic isolationNo current flow from one circuit to anotherSignal information passes from one circuit to another

3

Why Do Systems Need Isolation?

Non-Isolated System

HV Path

♦ A high-voltage breakdown path exists through the control circuitry

Hig

h Vo

ltage

4

Isolation Prevents Electrocution

♦ High voltage path is blocked because of high impedance between grounds

ISOLATOR

Very high impedance between grounds!

Hig

h Vo

ltage

5

Ground loops Common mode noise

Voltage transients Incompatible voltage levels

Other Isolator Applications

`

MCU or DSP

Bus Controller & Transceiver

SIGNALRETURN

(-) (+)

Ground Loop

Ground Potential Difference

Host Computer

6

Isolation Markets and Applications

Industrial

Automotive

Medical

Comm.

Computers& Office

EquipmentConsumer

♦ Broad market for isolation products; not just “power” systems

Isolation

7

Isolation Markets and Applications

Industrial

Automotive

Medical

Computer & Office Equipment

Communications

Consumer

•Automated test equipment•Fieldbus•Industrial communications•Industrial networking•Motor control•PLC input/output isolation•Power distribution systems•Power generation•Robotics•Switching panel•Switching power supplies•Test & measurement

•Hybrid electric vehicles•CANBus communications•IPM motor inverter drives•IPM DC-DC converters•Inverters for battery chargers•Battery/inverter voltage monitoring

•Defibrillators•ECG/EKG•Endoscopes•Magnetic resonance imaging•Patient monitoring

•Isolated input/output module•Isolated USB hub•Printers and plotters

•Automated meter reading•Digital cross connect•Distributed power architecture•PBX and central office•Power over Ethernet•Telephone switching equipment•Telephone terminal equipment•Wireless base station

•Air conditioning•Alarm systems•Audio & video equipment•Electronic gaming•Fitness equipment•Induction coolers•Plasma displays•Washing machines

8

Safety Standards Compliance

♦ Countries require compliance for certain equipment

♦ Creepage and clearance

♦ Safety Standards

Creepage Clearance

Note: other testing agencies exist (TUV…)

This is the customers requirement

ISOdriversSi841x/2x Si843x/4x Si823x

1&2 Channel 8SOIC

3&4 Channel 16WBSOIC

0.5/4A HS/LS 16 WBSOIC

UL UL1577 -- 2.5KVrms Basic 〇 〇 〇

-- 2.5KVrms Reinforced

CSA CSA/IEC 60950-1 400 Vrms 2.5KVrms Basic 〇 〇 〇

CSA/IEC 60950-1 130Vrms 2.5KVrms Reinforced 〇 〇

VDE DIN EN 60747-5-2 400 Vrms 4kVpk Basic 〇 〇 〇

DIN EN 60747-5-2 400 Vrms 4kVpk Reinforced

Insulation Type

IsolatorsTesting Agency Standard

Working Voltage

gTransient

Overvoltage

9

♦ Digitize sensor output from ADC in harsh environment♦ Isolate high-speed digital signals from noise-sensitive analog circuits

Serial Output ADC

Parallel Output ADC

Isolated Data Acquisition

SensorsMCU

or DSP

VCM = 600VDC

Parallel OutputADC

3.3V

IsolationDATA

CTL

DATA

CTL

10

Industrial (Serial Field Bus) Communication

♦ Central communication to distributed field devicesPROFIBUS - twisted pair serial (like RS485): 1.5 Mbps or 12 MbpsDeviceNet and others

♦ Application requirements: <25 Mbps, low prop delay, reliability

11

Industrial Communications—Isolated RS232/422, USB

♦ Isolation prevents common mode transients from corrupting data in a noisy environment

MCU/DSP

ISOLATION

ISOLATOR

ISOLATOR

D+

D-

USB I/O

RS232/422 USB

12

Industrial PLC I/O

♦ Isolates the low-voltage processor logic from drive voltages

Programmable Logic Controller I/O Unit

Logi

c ci

rcui

t

13

Automotive Isolation

♦ Hybrid electric cars, intelligent power module (IPM), digital signal isolation♦ CANBus comm., power transistor isolation, MCU/ADC/DAC digital isolation♦ Application requirements: wide temp range (-40 to 125° C), high reliability

M

Isolation

CANTransceiver

MCU

Other Devices

Isolation

UARTNetwork Controller

Bus Interface

Intelligent Power Module Automotive CANBus

14

Power Over Ethernet (PSE)

♦ Isolate I2C signal to 48 V power supply♦ Application requirements: 3.3 V/5 V, 1 Mbps

HostController

Hot SwapController

EthernetSwitch/

Hub

INT/

SDA

SCL

INT/

SDA

SCL

RJ4

5R

J45

RX

TX

15

Motor Control Isolation

♦ Many isolation paths—isolator, ISOdriver, current sensor opportunity♦ High performance motors require precision timing from MCU to power devices♦ Application requirements: short propagation delay, driving IGBT power devices

Motor Electronics Block Diagram

16

ISOdriver: High Integration, Performance, Features

♦ High-Side/Low-Side ISOdriver ♦ 4A peak drive current♦ Fast propagation time: 50ns♦ 2500Vrms isolation (600 VDC: in/out and out/out)

Si8230/3

INPUT DRIVER

UVLO

UVLO

GNDI

VDDI

INA

VDDA

VOA

GNDA

VOB

VDDB

GNDB

DISABLE

ISO

LATI

ON

DT

DRIVER

DRIVER

UVLO

ISO

LATI

ON

INB

INPU

T LO

GIC

OVERLAP PROTECTION

DEAD TIMEADJUST

CB

600 V max

VDDA

Q1

Q2

D1

C2

VDDB

C3

CONTROLLER

HIGH SIDE OUT

LOW SIDE OUT

DISABLE CONTROL

VDD

GND

VDD

C3

DRIVER

High voltage power stage

17

Features of Integrated ISOdriver Solution

FEATURE BENEFITHighest integration Smallest PCB footprintTwo-wire or PWM input versions Connects directly to controllers of all typesProgrammable dead time control Allows user to “tune” system for peak efficiencyOverlap protection Higher efficiency, greater safetyDISABLE input Facilitates local ON/OFF control/protectionInput & output UVLO Glitch-free start-up/shutdown

PWM output driving ISOdriver2-wire output driving ISOdriver

18

ISOdrivers: Fastest Propagation Time

♦ ISOdriver: 50 ns propagation time8x faster than opto + driversEnables faster control loop responseEnables greater system timing margin

ISOdriver vs. Opto + driver delay

Total Propagation Delay

19

Integrated Overlap Protection Improves Reliability

VIN

A

B

VOUT

Simple Buck Converter

SHOOT-THROUGH CURRENT

♦ Integrated overlap protection prevents ISOdriver from turning on both HS/LS transistors simultaneously

♦ Prolonged shoot-through current causes damage

20

Dead Time Adjust Optimizes System Efficiency

♦ Precise dead time adjustment optimizes efficiencyAdjusted through single resistor—prevents board redesignOptimizes efficiency by minimizing dead time (when Q1 & Q2 are off; Q2 on)

* Q2 RDSON = 5mΩ

A

B

Dead Time

Dead time Cannot = 0!!Must allow time for Q1 to completely turn off before Q2 turns ON!!

Simple Buck Converter

Q2 ON: Power loss = IOUT

2 x RDSON= 0.5W

Q2 OFF: Power loss = VT x IOUT = 7W!!!

21

ISOdriver vs. Opto-coupled Drivers

CONTROLLER

OUTH

High Side/Low Side Driver

GND

OUTL

VDD

VIN

VDD2

CBSTRAP

Opto Coupler

Opto Coupler

Isolation Barrier

Load

VDD1

Ground 1

Ground 2

Ground 2

Ground 2

Ground 2

VDD2

Ground 2

CONTROLLER

OUTH

Si823xISODriver

GND

OUTL

VDD

VIN

VDD2

CBSTRAP

Load

VDD1

Ground 1

Ground 2

Ground 2

Ground 2

Silic

on L

abs

RF

Isol

ator

Tec

hnol

ogy

Ground 1

VDD1

Integrated Isolator + Driver♦ Highest integration♦ Board space: 125mm2

♦ Fast propagation time: 50ns♦ Stable over temperature and age♦ 5ns channel to channel matching

Optocoupler + dual driver solution ♦ Many discrete components♦ Board space: 490mm2

♦ Slow propagation time: 400ns♦ Optocouplers vary with temp and age♦ 15ns channel to channel matching♦ Problematic EMI

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