AN799 Matching MOSFET Drivers to MOSFETs

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1、AN799MatchingMOSFETDriverstoMOSFETs2.PowerdissipationduetoquiescentcurrentdrawAuthor:JamieDunnoftheMOSFETdriver.MicrochipTechnologyInc.EQUATION2:INTRODUCTIONTherearemanyMOSFETtechnologiesandsiliconPQ=()IQH´DI+QL´()1D–´VDDprocessesinexistencetoday,withnewadvancesbeingmadeev

2、eryday.TomakeageneralizedstatementWhere:aboutmatchingaMOSFETdrivertoaMOSFETbasedIQH=Quiescentcurrentofthedriverwithonvoltage/currentratingsordiesizesisverydifficult,iftheinputinthehighstatenotimpossible.D=DutycycleoftheswitchingwaveformAswithanydesigndecision,therearemulti

3、plevari-IQL=QuiescentcurrentofthedriverwithablesinvolvedwhenselectingtheproperMOSFETtheinputinthelowstatedriverfortheMOSFETbeingusedinyourdesign.Parameterssuchasinput-to-outputpropagationdelay,3.Powerdissipationduetocross-conductionquiescentcurrent,latch-upimmunityanddrive

4、rcurrent(shoot-through)currentintheMOSFETdriver.ratingmustallbetakenintoaccount.PowerdissipationofthedriverwillalsoeffectyourpackagingdecisionEQUATION3:anddriverselection.P=CC´F´VThisApplicationNotediscussesthedetailsofMOSFETSDDdriverpowerdissipationinrelationtoMOSFETgateW

5、here:chargeandoperatingfrequency.ItalsodiscusseshowCC=Crossoverconstant(A*sec)tomatchMOSFETdrivercurrentdrivecapabilityandMOSFETgatechargebasedondesiredturn-onandAsdeducedfromtheequationsabove,onlyoneoftheturn-offtimesoftheMOSFET.threeelementsofpowerdissipationisduetotheMi

6、crochipoffersmanyvariationsofMOSFETdriversincharginganddischargingoftheMOSFETgatevariouspackages,whichallowsthedesignertoselectcapacitance.ThisportionofthepowerdissipationistheoptimalMOSFETdriverfortheMOSFET(s)beingtypicallythehighest,especiallyatlowerswitchingusedintheira

7、pplication.frequencies.POWERDISSIPATIONINAMOSFETInordertocalculateavalueforEquation1,thegatecapacitanceoftheMOSFETisrequired.ThegateDRIVERcapacitanceofaMOSFETiscomprisedoftwocapaci-CharginganddischargingthegateofaMOSFETtances:thegate-to-sourcecapacitanceandthegate-requires

8、thesameamountofenergy,regardlessofhowto-draincapacitance(MillerCapacitance).Acommonfastor