IGBT门极电阻设计

ApplicationNoteRevision:IssueDate:Preparedby:002007-11-12MarkusHermwilleKeyWords:IGBTdriver,gateresistor,selection,design,applicationGateResistor–PrinciplesandApplicationsIntroduction1IGBTSwitchingBehaviour2SwitchingBehaviourofFree-WheelingDiode4DrivingOutputStage4GateResistorDimensioning5MinimumGateResistance–MaximumGatePeakCurrent6PowerDissipation6PeakPowerCapability7ResistorType7DesignandLayout7Troubleshooting9SymbolsandTermsUsed9References10Thisapplicationnoteprovidesinformationontheuseofgateresistors(RGtocontrolIGBTswitching.Theinformationgiveninthisapplicationnotecontainstipsonlyanddoesnotconstitutecompletedesignrules;theinformationisnotexhaustive.Theresponsibilityforproperdesignremainswiththeuser.IntroductionTheswitchingbehaviourofpowersemiconductorsiscontrolledbythegatecapacitancerecharge.Thisgatecapacitancerechargemaybecontrolledviaagateresistor.Byusingatypicalpositivecontrolvoltage(VG(onof+15VtheIGBTisturned-onandturned-offatanegativeoutputvoltage(VG(offoftypically-5…-8…-15V.ThedynamicIGBTperformancecanbeadjustedbythevalueofthegateresistor.ThegateresistorinfluencestheIGBTswitchingtime,switchinglosses,reversebiassafeoperatingarea(RBSOA,short-circuitsafeoperatingarea(SCSOA,EMI,dv/dt,di/dtandreverserecoverycurrentofthefree-wheelingdiode.Ithastobeselectedandoptimizedverycarefullyinaccordancewiththeindividualapplicationparameters,e.g.IGBTtechnology,diode,switchingfrequency,losses,applicationlayout,inductivity/strayinductance,DC-linkvoltageanddrivercapability.Thecompletedesignofanapplicationmustbeviewedasawhole,withdueconsideringoftheabove-mentionedparameters.Interactiveeffectswithinthewholeapplicationmustbeevaluatedandaccommodated.www.S/Application/GateResistorApplicationNoteIGBTSwitchingBehaviourTheswitchingbehavioursettingofeachIGBTcanbeaffectedbytheexternalresistorRG.AstheinputcapacitanceofanIGBT,whichvariesduringswitchingtime,hastobechargedanddischarged,thegateresistorwilldictatewhattimeisneededtodothisbylimitingthemagnitudeofthegatecurrent(IGpulsesduringturn-onandturn-off.Duetotheincreaseinthegatepeakcurrent,whichisaffectedbyreducingtheresistorvalueRG(onandRG(off,theturn-onandturn-offtimewillbeshorterandtheswitchinglosseswillbereduced.Thefollowingdiagramsshowswitchinglossesandswitchingtimesdependingontheselectedgateresistorvalue.Whatneedstobeconsideredwhenreducingthevalueofthegateresistoristhedi/dtgeneratedwhenhighcurrentsareswitchedtoofast.Thisisduetostrayinductancepresentinthecircuit,whichproducesahighvoltagespikeontheIGBT.Thissurgevoltagecanbeestimatedusingthefollowingequation.ThiseffectcanbeobservedinthewaveformshownforIGBTturn-off.Theshadedareasshowtherelativevalueoftheswitchinglosses.Thetransientvoltagespikeontopofthecollector-emittervoltagemaydestroytheIGBT,especiallyinshort-circuitturn-offoperationwithahighdi/dt.Asshowninthefollowingdiagram,Vstraycanbereducedbyincreasingthevalueofthegateresistor.Thus,theriskofIGBTdestructionduetoovervoltagecanbeeliminated.AN-7003Intermsoftheinterlock/deadtimebetweenhighsideIGBT(TOPandlowsideIGBT(BOTinahalf-bridgeconfiguration,theinfluenceofthegateresistoronthedelaytimehastobeconsidered.AlargeRG(offincreasestheIGBTfalltime,whichiswhytheeffectivedeadtimemayexceedtheminimumdeadtime.Thisleadstoanincreasedshoot-throughtendency.Fastturn-onandturn-offleadstohigherdv/dtanddi/dtvaluesrespectively.Thus,moreElectromagneticEmissions(EMIareproducedandcanbringaboutcircuitrymalfunctioninapplication.Thefollowingtableshowstheinfluenceofdifferentgateresistorvaluesondi/dt.ThefollowingtableprovidesanoverviewoftendenciesinIGBTswitchingbehaviourcausedbychangesingateresistorvalues.Rating/CharacteristicsRGRGtontoffEonEoffTurn-onpeakcurrentTurn-offpeakcurrentdiodedv/dtdi/dtVoltagespikeEMInoiseApplicationNoteSwitchingBehaviourofFree-WheelingDiodeTheswitchingbehaviourofthefree-wheelingdiodeisalsoaffectedbythegateresistorandlimitstheminimumvalueofthegateresistance.Thismeansthattheturn-onswitchingspeedoftheIGBTcanbeonlyincreaseduptoalevelcompatiblewiththereverserecoverybehaviourofthefree-wheelingdiodebeingused.AdecreaseinthegateresistorincreasesnotonlytheovervoltagestressontheIGBT,butalsoonthefree-wheelingdiodescausedbytheincreaseddiC/dt.Thefollowingdiagramdepictsthetypicaldependencyofthefree-wheelingdiodereverserecoverycurrentIRRMondiF/dt,determinedbythecontrolofthegivengateresistorRG(onoftheIGBT.ThereverserecoverycurrentincreaseswiththecommutationspeeddiF/dt.AnincreaseinIRRMwillalsocausehigherturn-offpowerdissipationinthefree-wheelingdiode.DiodePeakReverseRecoveryCurrentvs.di/dtandRG(e.g.SKM200GB128D&SoftRecoveryBehaviourAN-7003GateResistorDimensioningAgateresistormustdemonstrateoptimumswitchingbehaviourwithregardtolowswitchinglosses,noIGBTmoduleoscillation,lowdiodepeakreverserecoverycurrentandmaximumdv/dtlimitation.Somehintsongateresistordimensioningaregivenbelow:Typically,IGBTmoduleswithalargecurrentratingwillbedrivenwithsmallergateresistors;similarly,smallIGBTmoduleswillrequirelargergateresistors.Generally,thevalueofanoptimisedgateresistorwillbesomewherebetweenthevalueindicatedintheIGBTdatasheetandroughlytwicethisvalue.Thisisapplicableformostapplications.ThegateresistorvaluespecifiedintheIGBTdatasheetistheminimumvalue;twicetheratednominalcurrentcanbesafelyswitchedoffundertheconditionsspecified.Inpractice,thegateresistorvalueintheIGBTdatasheetcannotalwaysbeachievedduetodifferencesbetweenthetestcircuitryandtheindividualapplicationparameters.Theroughvaluementioned(i.e.twicethedatasheetvaluemaybetakenasastartingpointforoptimisation,i.e.toreducethegateresistorvalue.Theonlywaytoascertainthefinaloptimisedvalueistotestandmeasurethefinalsystem.Inmostapplications,theturn-ongateresistorRG(onissmallerthantheturn-offgateresistorRG(off.Dependingontheindividualparameters,RG(offcanberoughlytwicetheRG(onvalue.Itisimportanttominimizeparasiticinductanceinapplications,especiallyintheDC-linkcircuit.Thisisnecessarytokeeptheturn-offovervoltageattheIGBTwithinthelimitsspecifiedintheIGBTdatasheet,particularlyinshort-circuitconditions.Asimplewayofreducingtheovervoltageinshort-circuitconditionsistouseasoftturn-offcircuit,forexample.Intheeventofashort-circuit,thesoftturn-offcircuitincreasestheresistanceinserieswithRG(offandturnsofftheIGBTmoreslowly.TheSEMIKRONIGBTdriversolutionSKYPER®32PRORfeaturesthissoftturn-offfunction.ThedatasheetforthisdriverisavailableontheDriverElectronicsproductpageatwww.SEMIKRON.com.Pleasenote:Theselectedgateresistorshouldbevalidatedbytheuser’stechnicalexpertsforeachapplication.ApplicationNoteMinimumGateResistance–MaximumGatePeakCurrentThegateresistancedeterminesthegatepeakcurrentIGM.Increasingthegatepeakcurrentwillreducetheturn-onandturn-offtimeaswellastheswitchinglosses.Themaximumvalueforthegatepeakcurrentandtheminimumvalueforthegateresistor,respectively,aredeterminedbytheperformanceofthedriveroutputstage.Inthedatasheetofadriveramaximumpeakcurrentisgiven,asistheminimumvalueforthegateresistor.Thesevalueshavetobeconsideredtoavoiddriverdamage.Inpractice,thegatecurrentmightbesomewhatsmallerduetotheIGBTmodule'sinternalresistorRG(intandinductancesinthegatecontrolpath.TheRG(intvalueisindicatedintheIGBTdatasheet.GateCurrentCalculationAN-7003PeakPowerCapabilityDuringoperation,thegateresistorhastowithstandacontinuousflowofpulses.Therefore,thegateresistorhastohaveacertainpeakpowercapability.Onepossiblewayofdeterminingthiscapabilityistocalculatethepulseloadpowerandusethediagramforcontinuouspulseloadsshowninthedatasheetofaresistor.ContinuousPulseLoad=f(tpEstimationofPulseLoadSource:Thepulseloadcanbecalculatedasfollows:G2GMPULSERIP×=ResistorTypeThegateresistormustmeetcertainperformancerequirementsandhavecertainfeaturesinordertobeabletowithstandthesubstantialloadthatoccursinapplication.Thefollowingtableshowsthemainfeaturesofagateresistorandanexampleofasuitableresistor.FeaturesofGateResistorSurgeproofMetalfilmLowtemperaturecoefficentTighttolerancesExcellentstabiltyindifferentenvrionmentalconditionsE.g.:MINI-MELFresistor,MELFresistorDesignandLayoutDuetothesubstantialloadonthegateresistors,theuseofresistorsinparallelisadvisable.Thiswouldproducearedundancy,enablingtemporaryoperationwithhigherswitchinglossesshouldonegateresistorbedamaged.Theperformanceofeachparalleledresistorinrelationtopowerdissipationandpeakpowercapabilitymustbedesignedformaximumgatecurrentinapplication.Usinggateresistorsinparallelalsohelpsimprovethermalspreading.Thelayoutwithgateresistorsinparallelmustbesuchthatexcessiveheatproducedbythegateresistorsdoesnotoverheatcomponentsmountednearby.Sufficientlargecoolingareasforthegateresistorsmustbegivendueconsiderationinthelayout.Suitableheatsinksontheprintedcircuitedboardcanbeusedtobringaboutbettercooling.Anexamplelayoutwithcoolingareasforparallelgateresistors(redandgreenareasisshownbelow.ApplicationNoteLayoutwithGateResistorsinParallelTopLayerBottomLayerLayoutextractfromEvaluationBoard1SKYPER®32PRO.Thetechnicaldocumentationwithopensourcedesign(e.g.schematic,layout,partslistofthisboardisavailabeontheDriverElectronicsproductpageatwww.SEMIKRON.com.RG(on=R251//R252//R253RG(off=R254//R255//R256ThedistancebetweenthegateresistorcircuitandtheIGBTmoduleshouldbekeptasshortaspossible.Longdistancesleadtohigherinductanceinthegate-emitterpath.CombinedwiththeinputcapacitanceoftheIGBT,thiswiringinductanceformsanLCcircuit.Thiscircuitmightcreateoscillation,whichcanbehigherthanthemaximumpermissiblegatevoltage.Thisoscillationcanbedampedbyusingagateresistorwhichislargerthantheminimumgateresistor,calculatedasfollows.ApplicationLink:FurtherdesigntipsaregivenintheApplicationNoteAN-7002"ConncectionofGateDriverstoIGBTandController".ThisapplicationnoteisavailableontheDriverElectronicsproductpageatwww.SEMIKRON.com.AN-7003TroubleshootingThefollowingtabledescribespossibleproblemsandtheireffectswithregardtogateresistors.Itshouldassistinpinpointingpossiblecausesandeffects.ProblemEffectandActionIncreasedswitchinglossesTheselectedgateresistorvalueistoohigh,causingexcessivelosses.Thegateresistorshouldbereduced,bearinginmindtheswitchingperformanceofthewholeapplication.ExcessivevoltagespikeatIGBTInductanceintheapplication(DC-linkistoohighorasmallturn-offgateresistorisused,leadingtoahigherdi/dt.Theinductanceshouldbeminimizedortheturn-offgateresistorincreased.Toreducevoltagespikeintheeventofashort-circuit,asoftturn-offcircuitmaybeused.Overheated/burnedgateresistorThepowerdissipationaswellaspeakpowercapabilityoftheresistorisnotsufficient.Anon-surge-proofresistorisinuse.EMInoisesVerysmallgateresistorsareused,leadingtohigherdv/dtordi/dtvalues.Asaresult,moreEMIisproduced.ToohighagateresistancevaluecausestheIGBTtooperateforalongtimeinlinearmodeduringswitchingandfinallyresultsingateoscillation.OscillationatthegateWiringbetweengateresistorandIGBTmoduleistoolong.Thisleadstohigherinductanceinthegate-emitterpathandforms-withtheinputcapacitanceoftheIGBT-aresonantcircuit.Theoscillationcanbedampedbyshorterwiring.Themaincurrentiscoupledinductiveintothecontrolcircuit.Avoidparallelgatewirestomainterminals.Usetwistedwires.SymbolsandTermsUsedSymbolTermCiesInputcapacitanceIGBTdiC/dtRateofriseandfallofcollectorcurrentdiF/dtRateofriseandfalloftheforwardcurrent(diodedvCE/dtRateofriseandfallofcollector-emittervoltageEoffEnergydissipationduringturn-offtimeEonEnergydissipationduringturn-ontimefswSwitchingfrequencyICCollectorcurrentIGGatecurrentIGMPeakgatecurrentIGRMSEffectivevalueofgatecurrentIrrReverserecoverycurrentIRRMPeakreverserecoverycurrentLσStrayinductanceLwireInductanceofwiringPGPowerdissipationingateresistorPPULSEPulseloadApplicationNoteRGGateresistorRG(intIGBTmoduleinternalgateresistorRG(minMinimumgateresistorRG(offTurn-offgateresistorRG(onTurn-ongateresistortTimetswSwitchingtimeTTimeperiodtpPulsedurationVCECollector-emittervoltageVGGatevoltage(outputdriverVG(offTurn-offgatevolt