hujinyi：
Fig.1.ThebestMOSFETdriversforhigh-speedswitchingconsistofacombinationbipolarandMOSprocess.TheMOSsectionisplacedinparallelwitheachbipolardevicetoachievetruerail-to-railswitchingbetweenVDDandground.TheresultisasuperiorMOSFETdriveroptimizedforhigh-speedswitchingandtrulyratedtodeliverthefull-currentspecifiedonthedatasheet.InternallyregulatedoradjustablegatedriveSomeMOSFETdriversuseafixedinternalregulatortosettheamplitudeofthegatedrivevoltage.InternallyregulatedgatedrivesshouldbeconsideredwhentheVDDsupplyvoltagetothedriverICisnotwellregulated.TheadvantageisthatthegatedriveamplitudeiswellregulatedandcanbecloselymatchedtoapowerMOSFETofferingoptimalswitchingresults.However,asthegate-to-sourcevoltageofapowerMOSFETisincreased,theon-resistanceisdecreasedresultinginlowerpowerdissipationfromconductionlosses.Conversely,asthegate-to-sourcevoltageisincreased,thepowerlossesassociatedwithgatechargearealsoincreased.Therefore,forconvertersrequiringhighestefficiency,suchasvoltage-regulator-moduleapplications,aMOSFETdriverwithanadjustablegatedrivevoltagemightbalancethegatechargelossesagainstconductionlossesmoreefficiently.PropagationdelayPropagationdelayisthetimeittakestopassasignalfromthedriver'sinputtooutput.WhilepropagationdelayscanaffectthetimingbetweenthePWMandthepowerMOSFET,thedelayisnotaprimaryconcernbecauseitisnormallyaccountedforwithintheconverter'scontrolloop.Forisolatedconvertersusingaprimary-sidePWMcontrollerandasecondary-sidesynchronousrectifierMOSFETdriver,propagationdelaycansignificantlyaffectthetimingoftheprimarytothesecondary.ArequirementforthesetypesofconvertersisthatthetotaldelaytothesecondarysynchronousrectifiersmustbelessthanthedelayfromthePWMthroughthepowertransformer.Usingasecondary-sideMOSFETdriverwithapropagationdelaylargerthantheprimary-sidePWMtoMOSFETdelaycanmakeitdifficulttooptimizethetimingbetweentheprimaryandsecondary.DeadtimecontrolForsynchronousbuckdc/dcconverterapplications,thehigh-sideandlow-sideMOSFETsmustnotbeallowedtoconductsimultaneouslyordestructive"shoot-through"currentscanresult.ThereforeanimportantconsiderationforthesetypesofMOSFETdriversisdeadtimecontrol.Currentdriversofferauser-programmablefixeddelaybetweenthetwodrivesignalsofasynchronousbuck.Theadvantageofthisapproachliesinitssimplicity.Thedisadvantageisthatprogrammingthedeadtimelongenoughtoensurethatcrossconductionwillnotoccurunderalloperatingconditionsresultsinadditionalbody-diodeconductionlossesinthelow-sidesynchronousMOSFET.Others梥uchastheTPS2838/9synchronousbuckdrivers梪seanadaptivegatedrivetechniquetoactivelyadjusttheamountofdeadtimebetweenthehigh-sideandlow-sideMOSFETs.Adaptivegatedrivesensesthedrain-to-sourcevoltageofthelow-sideMOSFETwhileactivelyadjustingthedeadtimetoreducebody-diodeconductionlossesandavoidcross-conduction.Adaptivegatedriveofferssignificantimprovementsoverfixed-delay,butstillsuffersfromthefactthatsomebody-diodeconductionisinevitableduetofinitepropagationdelaysbetweenthetimethatbody-diodeconductionisdetectedandthegatedrivesignalisadjusted.Newdriverstodayalsouseapredictivegatedrivetoovercomethepropagationdelaysassociatedwithadaptivegatedrive.Predictivegatedrivetechnologyisadigital-controltechniquethatvirtuallyeliminatesbody-diodeconductionwhileoptimizingdead-timetogivethehighestpossibleefficiency.PackagingAswithanypowermanagementIC,thejunctiontemperatureofaMOSFETdrivermustbekeptsafelywithinratedlimitsunderalloperatingconditions.Industry-standardpackagessuchasDIP,SOIC,andTSSOParepopularconsiderations,buthigh-currentMOSFETdriversusedinhigh-frequencyapplicationsrequirecarefulconsiderationgiventoadvancedpackagingtechniques.Today'sMOSFETdriversareplacedinTSSOPswithanexposedleadframediepadonthebottomofthepackage.ThisisknownasaPowerPadTSSOP,orHTSSOP,offeringthermalimpedancewithajunction-to-caseratingaslowas2°C/W.ComparedwithaTSSOPwithoutPowerPadoperatingatsimilarjunctiontemperatures,thelowerthermalimpedanceoftheHTSSOPmeansmorepowercanbedissipatedwithinacomparablysizedpackage.Forapplicationswhereminimizingparasiticeffectssuchasstraycapacitanceandleadinductancearecrucialforswitchingperformance,theQFNpackageisamust.QFNpackageshavenomeasurableleadinductance,makingthemidealforhigh-frequencyconverterdesigns.AdditionalconsiderationsSecondaryMOSFETdriverICconsiderationswouldincludeadditional"featuresofconvenience"notassociatedwithdriverperformanceenhancement.ThesemightincludesuchfeaturesasEN(Enable),overvoltageprotection,thermalshutdown,orovercurrentprotection.BecauseMOSFETdriverICsareusedinavarietyofisolatedandnonisolatedpowerconverterapplications,afinalnoteofconsiderationwouldbehavingaccesstoasolidknowledgebaseoftechnicalsupport.Thissupportcanoftenmeanthedifferencebetweendesignsuccessandfailure.