Fundamentals of MOSFET and IGBT Gate Driver Circuits ...

1 1 SLUA618A March2017 RevisedOctober2018 SubmitDocumentationFeedbackCopyright 2017 2018,TexasInstrumentsIncorporatedFundame ntalsof MOSFETand IGBTGateDriverCircuitsApplicationReportS LUA618A March2017 RevisedOctober2018 Fundamentalsof MOSFETand IGBTGateDriverCircuitsLaszloBaloghABSTRA CTT hemainpurposeof this applicationreportis to demonstratea systematicapproachto designhighperformancegatedrivecircuitsfo r is an informativecollectionoftopicsofferinga one-stop-shopping to solvethe ,it shouldbeof interestto powerelectronicsengineersat all levelsof mostpopularcircuitsolutionsand theirperformanceare analyzed,includingthe effectof parasiticcomponents,transientand morecomplexproblemsstartingwithan overviewof MOSFET technologyand groundreferencedand highsidegatedrivecircuits,AC coupledand transformerisolatedsolutionsare describedin specialsectiondealswith the gatedriverequirementsof theMOSFETsin moreinformation,see the Overviewfor ,step-by-stepnumericaldesignexamplescomp lementthe documentis also availablein Chinese.

2 MOSFET IGBT of March2017 RevisedOctober2018 SubmitDocumentationFeedbackCopyright 2017 2018,TexasInstrumentsIncorporatedFundame ntalsof MOSFETand for a Functionof RestoreCircuitin ControlTransmissionWithOne ControlTransmissionWithOne trademarksare the propertyof is an acronymfor MetalOxideSemiconductorFieldEffectTransi storand it is the keycomponentin high frequency,high efficiencyswitchingapplicationsacrossthe surprising,but FET technologywas inventedin 1930,some20 yearsbeforethe first signallevelFET transistorswerebuilt in the late 1950 s whilepowerMOSFET shavebeenavailablefromthe mid 70 s.

3 Today,millionsof MOSFET transistorsare integratedin modernelectroniccomponents,frommicroproc essors,through discrete focusof this topicis the gatedriverequirementsof the powerMOSFETin bipolarand the MOSFET transistorsexploitthe ,bothtype oftransistorsare chargecontrolleddevices,whichmeansthat theiroutputcurrentis proportionalto thechargeestablishedin the semiconductorby the usedasswitches,bothmustbe drivenfroma low impedancesourcecapableof sourcingand sinkingsufficientcurrentto providefor fast insertionand extractionof the pointof view,theMOSFET shaveto be drivenjust as hard duringturn-onand turn-offas a bipolartransistorto ,the switchingspeedsof the bipolarand MOSFET devicesarecloseto identical,determinedby the time requiredfor the chargecarriersto powerdevicesare approximately20 to 200 picosecondsdependingon the size of the March2017 RevisedOctober2018 SubmitDocumentationFeedbackCopyright 2017 2018.

4 TexasInstrumentsIncorporatedFundamentals of MOSFETand IGBTGateDriverCircuitsThe popularityand proliferationof MOSFET technologyfor digitaland powerapplicationsis drivenby twoof theirmajoradvantagesoverthe of thesebenefitsis the easeof use ofthe MOSFET devicesin high MOSFET transistorsare simplertodrivebecausetheircontrolelectro deis isolatedfromthe currentconductingsilicon,thereforea continuousON currentis not MOSFET transistorsare turned-on,theirdrivecurrentis ,the controllingchargeand accordinglythe storagetime in the MOSFET transistorsis basicallyeliminatesthe designtrade-offbetweenon statevoltagedrop,whichis inverselyproportionalto excesscontrolcharge,and a result, MOSFET technologypromisesto usemuchsimplerand moreefficientdrivecircuitswith significanteconomicbenefitscomparedto ,it is especiallyimportantto highlightfor powerapplications,that MOSFET shavea voltagedropacrossthe drainsourceterminalsof a MOSFETis a linearfunctionof the currentflowingin the linearrelationshipis characterizedby the RDS(on)

5 Of the MOSFET andknownas the constantfor a givengate-to-sourcevoltageand temperatureof the opposedto the C temperaturecoefficientof a p-n junction,the MOSFET sexhibita positivetemperaturecoefficientof C to 1%/ C. This positivetemperaturecoefficientof the MOSFET makesit an idealcandidatefor paralleloperationin higherpowerapplicationswhereusinga singledevicewouldnot be practicalor to the positiveTC of the channelresistance,parallelconnectedMOSFE T stendto sharethe currentsharingworksautomaticallyin MOSFET ssincethe positiveTC acts as a devicecarryinga highercurrentwill heatup more don t forgetthat the drainto sourcevoltagesareequal and the highertemperaturewill increaseits RDS(on)

6 Increasingresistancewill causethecurrentto decrease,thereforethe temperatureto ,an equilibriumis RDS(on)valuesand differentjunctionto ambientthermalresistancescan causesignificant up to 30% errorin +++Substraten EPI layerGATESOURCEDRAIN ppnnn+++Substraten EPI layerGATESOURCEDRAINpp++(a)(b)nn++Substr atepGATESOURCEDRAINpn(c) March2017 RevisedOctober2018 SubmitDocumentationFeedbackCopyright 2017 2018,TexasInstrumentsIncorporatedFundame ntalsof MOSFETand manufacturershavetheiruniquetwiston how to manufacturethe best powerMOSFETs,but allof thesedeviceson the marketcan be categorizedinto PowerMOSFETD eviceTypesDouble-diffusedMOStransistorsw ereintroducedin the 1970 s for powerapplicationsand evolvedcontinuouslyduringthe self-aligningprocesses.

7 Higherdensityintegrationand rapidreductionin next significantadvancementwas offeredby the V-grooveor trenchtechnologyto furtherincreasecell densityin betterperformanceand denserintegrationdo not comefree;however,as trenchMOSdevicesare moredifficultto lateralpowerMOSFET shavesignificantlylowercapacitances,ther efore,they can switchmuchfasterand they requiremuchless March2017 RevisedOctober2018 SubmitDocumentationFeedbackCopyright 2017 2018,TexasInstrumentsIncorporatedFundame ntalsof MOSFETand numerousmodelsavailableto illustratehow the MOSFET works,neverthelessfindingthe rightrepresentationmightbe the MOSFET manufacturersprovideSpiceand/orSabermode lsfor theirdevices.

8 But thesemodelssay very little aboutthe applicationtrapsdesignershaveto face to solvethe reallyusefulMOSFET modelthat describesall importantpropertiesof the devicefroman applicationpointof viewwouldbe very the otherhand,very simpleand meaningfulmodelscan bederivedof the MOSFET transistorif we limit the applicabilityof the modelto first modelin Figure2 is basedon the actualstructureof the MOSFET deviceand can be usedmainlyfor DC MOSFET symbolin Figure2a representsthe channelresistanceand theJFET correspondsto the resistanceof the length,therefore,the resistanceof the epilayeris a functionof the voltageratingof the deviceas high can be usedvery effectivelyto modelthe dv/dtinducedbreakdowncharacteristicof a showsbothmainbreakdownmechanisms,namelyt he dv/dtinducedturn-onof the parasiticbipolartransistorpresentin all powerMOSFET sand the dv/dtinducedturn-onof the channel,as a functionof practicallyimmuneto dv/dttriggeringof theparasiticnpn transistordue to manufacturingimprovementsto reducethe resistancebetweenthe baseand mustbe mentionedalso that the base collectorjunctionis the famousbodydiodeof the (a)

9 DSG(b)DSG(c) March2017 RevisedOctober2018 SubmitDocumentationFeedbackCopyright 2017 2018,TexasInstrumentsIncorporatedFundame ntalsof MOSFETand IGBTGateDriverCircuitsFigure2. PowerMOSFETM odelsFigure2c is the switchingmodelof the mostimportantparasiticcomponentsthatinfl uencesswitchingperformanceare shownin this , whichis dedicatedto the switchingprocedureof the the MOSFETis considered,the goal is to switchbetweenthe lowestandhighestresistancestatesof the devicein the practicalswitchingtimesofthe MOSFETs(approximately10 ns to 60 ns) is at leasttwo to threeordersof magnitudelongerthanthetheoreticalswitchi ngtime (approximately50 ps to 200 ps)

10 , it seemsimportantto the MOSFET modelsin Figure2, notethat all modelsincludethreecapacitorsconnectedbet weenthe threeterminalsof the ,the switchingperformanceofthe MOSFET transistoris determinedby how quicklythe voltagescan be ,in high speedswitchingapplications,the mostimportantparametersare the parasiticcapacitancesof the of thesecapacitors,the CGSand CGDcapacitorscorrespondto the actualgeometryof the devicewhilethe CDScapacitoris the capacitanceof the basecollectordiodeof theparasiticbipolartransistor(bodydiode) .= = DS,specGD,aveRSS,specDS,offDS,specOSS,av eOSS,specDS,offVC2 CVVC2 CV=+ GD,eqvfs LGDC(1 g R ) C==-=-GDRSSGSISSRSSDSOSSRSSCCCCCCCCCDS,0 CDSK V2DS| + GD,0GD1 DSCC1 K March2017 RevisedOctober2018 SubmitDocumentationFeedbackCopyright 2017 2018,TexasInstrumentsIncorporatedFundame ntalsof MOSFETand IGBTGateDriverCircuitsThe CGScapacitoris formedby the overlapof the sourceand channelregionby the definedby the actualgeometryof the regionsand staysconstant(linear) CGDcapacitoris the resultof two of it is the overlapof