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Common Mode Chokes in CAN Networks

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ApplicationReport

SLLA271–January2008

CommonModeChokesinCANNetworks:

SourceofUnexpectedTransients

Ole-KristianSkroppaandScottMonroe

ABSTRACT

Common-modechokesarefrequentlyusedinautomotiveCANnetworkstoincrease

systemreliabilitywithrespecttoelectromagneticcompatibility(EMC).Electromagnetic

interferenceemittedfromanElectronicControlModule(ECU)throughtheCAN

transceivercanbefiltered,thuslimitingunwantedhigh-frequencynoiseonthe

communicationbus.Anotherreasonforusingacommon-modechokeisattemptingto

improvethesusceptibility(immunity)ofthetransceivertoelectromagneticdisturbances

onthebus.

Whiletheabovementionedeffectsofthecommon-modechokearebeneficial,

unexpectedresultscanoccurundercertainconditions.EMCsusceptibilitycanbe

degradedinsomefrequencyranges,bussignalintegrityworsened,andextremelyhigh

transientvoltagesunderbus-failureconditionscanbegenerated,which,intheworst

case,canleadtodamageintheCANtransceiverandothernetworkcomponents.

Careshouldbetakeninthechoiceofcommon-modechoke(windingtype,coretype,

andinductancevalue),alongwiththeterminationandprotectionschemeofthenode

andbustopreventdamagetotheCANtransceiverorothernetworkcomponents.This

applicationreportaddressessomeofthesystem-levelconsiderationstotakeinto

accountduringnetworkandnodedesign.

Contents

1ApplicationDescription.............................................................................22ApplicationHint1:TransientProtectorLocationinSystem...................................4

3ApplicationHint2:Common-ModeChokeChoice.............................................5

4Summary.............................................................................................6

ListofFigures

1SimplifiedSchematicofTypicalCAN(Terminating)NodeWithOptionalBusComponents.........................................................................................2

2SimplifiedSchematicofTypicalCAN(Nonterminating)NodeWithOptionalBusComponents.........................................................................................2

3SimplifiedCANNodeTestSetup.................................................................3

4CANLMeasuredatBus(Green)andTransceiver(Blue)atShort-CircuitImpact.........3

5StartofCommunicationDuringDCShortCircuitatBus(Green)andTransceiver(Blue)3

6CANNodeWithTransientProtectorsatTransceiverPins....................................4

7SBMJ30CATVSDiodesProtectingTransceiver...............................................4

8VC060314A300RPVaristorsProtectingTransceiver..........................................4

ListofTables

1MeasurementofTransientsforDifferentCommon-ModeChokesWithCANLShortedto12V.....................................................................................5

2MeasurementofTransientsforDifferentCommon-ModeChokesWithCANHShortedto12V.....................................................................................6

SLLA271–January2008Common-ModeChokesinCANNetworks:SourceofUnexpectedTransients1

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1ApplicationDescription

TXD

GND

VCC

RXDS/STB

CANH

CANL

VREF/SPLITCANTransceiver

LCMDESDCBUS

CTermRTerm_1

RTerm_2

DESDCBUS

TXD

GND

VCC

RXDS/STB

CANH

CANL

VREF/SPLITCANTransceiver

LCMDESDCBUS

DESDCBUSApplicationDescription

ManymodernautomotiveCANtransceiversareoptimizedforEMCandawidecommon-modeoperating

rangetoallowuseinautomotiveCANsystemswithoutacommon-modechoke.However,forvarious

reasons,theCANnetworkarchitectureschemebeingusedmaysometimesrequiretheiruse,ortheymay

beusedsimplyoutofperceivedneed.

Ingeneral,common-modechokesmayintroducesignal-integrityissuesandotherunexpectedresultsin

theCANnetwork.Oneofthemostsevereunexpectedconsequencesfromcommon-modechokeuseis

theextremelyhightransientvoltagesthatmaybegeneratedbytheinductiveflybackduringashortcircuit

ofaCANbuslinetoadcvoltage.Asthetransceiverdrivesthebuslevelfromdominanttorecessiveor

recessivetodominantduringthisshort-circuitcondition,thechangeincurrentthroughthecommon-mode

chokemayflybackinexcessof65V.Theexacttransientsthataregeneratedhighlydependonthe

common-modechoke(windingtype,coretype,andinductancevalue)butarealsoinfluencedbythe

termination,busload,dcshort-circuitvoltagelevel,andshortcondition,cabling,andotherparasiticeffects

onthePCBandwiringharness.Caremustbetakentominimizetheexposureofexcessivetransientsto

theCANtransceiverandothernetworkcomponents.Anytransientoutsidethemaximumoperatingrange

ofthetransceiver,typically–27Vto40V,especiallyforextendedperiods,mayleadtodegradeddevice

reliabilityorevendamage.

AsimplifiedschematicofatypicalCANnode(terminating)includingacommon-modechokealongwith

otherbuscomponentsisshowninFigure1.Followingthechokeinthesignalpathtothebusisthe

optionalterminationcircuit.Ifthenodeisastubnode(nonterminating),theterminationcircuitmayconsist

合集下载

B82793S0513N201;B82793C475N265;中文规格书,Datasheet资料

B82793S0513N201;B82793C475N265;中文规格书,Datasheet资料

¤󰀂EPCOS AG 2010. Reproduction, publication and dissemination of this publication, enclosures

hereto and the information contained therein without EPCOS’ prior express consent is prohibited.Data and signal line chokes

Common-mode chokes, ring core

0.005 … 47 mH, 100 … 1200 mA, 60 °C

Series/Type:B82793C0/S0

Date:July 2010

/

207/10Please read Cautions and warnings and

Important notes

at the end of this document.Rated voltage 42 V AC/80 V DC

Rated inductance 0.005 mH to 47 mH

Rated current 100 mA to 1200 mA

Construction

■Current-compensated double choke

■Ferrite core

■LCP case (UL 94 V-0), silicone potting

■Bifilar winding (B82793C0)

■Sector winding (B82793S0)

Features

■High rated currents, reduced components height

■Qualified to AEC-Q200 (L d󰀂4.7 mH)

■Suitable for reflow soldering

■RoHS-compatible

Function

Coax Common Mode Noise Filters, Mini-Choker, Mini

Coax Common Mode Noise Filters, Mini-Choker, Mini

COAX COMMON MODE

NOISE FILTERS,

MINI-CHOKER, MINI BALUN

PRODUCT MANUAL

© Palomar Engineers, Inc., 1965-2020

Coax Common Mode Noise Filter/Mini-Balun Models

Model # Range (MHz) PEP (ICAS) CMRR Size/notes

CMNF-500-50

MC-1-500 1.8-65 500 20-38

dB 3” x 2” x 1”, SO-239 I/O

MB-1-500-50 1.8-65

MHz 500 20-38

dB 3” x 2” x 1”, SO-239 In,

Balanced output

CMNF-500-75 or

CMNF-TV 1.8-65 500 20-38

dB 3” x 2” x 1” ”, “F” connector

I/O

CMNF-500-VHF 15-180 250 20-30

dB 3” x 2” x 1” ”, SO-239 I/O

CMNF-1500HF 1.8-65 1500 20-38

dB 4” x 4” x 2” ”, SO-239 I/O

CMNF-5000HF 1.8-65 5000 20-38

dB 4” x 4” x 2” ”, SO-239 I/O

© Palomar Engineers, Inc., 1965-2020

The Problem:

Common mode current induced by radiated sources (plasma TV, routers, computers, transmitters, etc.) can be

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