Adaptive Constant On-Time (D-CAPTM - Texas Instruments

1 1 Introduction+++VrefErrorAmplifierPWMC omparatorVrampC1C2R2 GateDriversUGLGR3 VINVoutCoLoC3R1 ApplicationReportSLVA281B July2007 RevisedDecember2007 AdaptiveConstantOn- time (D-CAP ) ,currentmode,constanton-timecontrol,anda daptiveontimecontrol(D-CAP mode)arediscussedindetailintermsoftheirc ontrolmethods, modeisstudied, ,currentmode,hystereticmode,constanton-t imemode,constantofftimemode,andadaptiveo n-timemode(D-CAP mode). [1] , July2007 RevisedDecember2007 AdaptiveConstantOn- time (D-CAP ) +++GateDriversVrefErrorAmplifierPWMC omparatorUGLGC2R2R1 VINVoutCoLoCurrentRampLoILoadITonVrefTon is triggered when Vodeclines to Vref On-Time ControlQ2 DRVHDRVLOne , (DCM) ,thehysteresiscontrolmodeorpulsefrequenc ymodulation(PFM)isusedatDCMtoreducethesw itchingloss,gatedriveloss, (D-CAP )ControlStudyinNotebookApplicationsSLVA2 81B July2007 V+12%Current V+12%CC_+_++_+_+_+_+_+ (VCC VTRIP1 VCCLSD TripHSD Trip VTRIP1)

2 ,Inordertoachievegoodlightloadefficiency , ,duringthemodetransition, , , , , , (D-CAP mode)isabletodynamicallyadjusttheon- time durationbasedontheinputvoltage,outputvol tage, , July2007 RevisedDecember2007 AdaptiveConstantOn- time (D-CAP ) ComparatorFBRefPWM LatchSRQIon = Vin/RonOn- time TimerConIoffCoffMinimum Off- time TimerSRQZC LatchZero-Crossing ComparatorLow-Side DriverM2 VDDVDDHigh-Side DriverM1 VINC ross Conduction ModeOperation[3] ModeBlockDiagramD-CAP modemeansDirectconnectiontotheoutputCAPa citorBasicOperationPrincipleAtthebeginni ngofeachcycle,thehighsideMOSFET(M1) , (M2) (D-CAP )ControlStudyinNotebookApplicationsSLVA2 81B July2007 (s)+1s RESR Co(3)IoR1R2 PWMVREFC ontrolLogicandDriverVinLxILIcVcVoRLESRCo PWMVREFC ontrolLogicandDriverVinLxILVxRsVoCoRLIoI ntroductionTypically, mode, , , , ,theoutputvoltageisgivenby:Vo=Vc+IC ESR=const.

3 (1)Figure9 ,thevoltagebeforethesensingresistorisgiv enby:Vx=Vo+IL Rs=const.(2)Basically, ,thismeansthatD-CAP July2007 RevisedDecember2007 AdaptiveConstantOn- time (D-CAP ) swKu12p RESR Co(4) ModeOutput Ripplet0 NoiseTopMOSFETD river SignalBottomMOSFETD river SignalOutput Ripplet0 Noiset0t1x(5) , , , , , ,duetonoiseonthedownslopeoftheoutputripp le, , ,whyaremostripplemodeconvertersrequiring theminimumamountofoutputrippleasstatedin manyofourcompetitor'sdatasheets? ,byincreasingthedownslopeoftheoutputripp le, (D-CAP )ControlStudyinNotebookApplicationsSLVA2 81B July2007 x VoEsr=dtL(6)-Esr x Vo x dtEsr x di =L(7)-Esr x VoR2Sr =xLR1 + R2(8)sinceR2 Vref = Vo xR1 + R2-Esr x VrefSr =L(9) ,inorderfortheripplemodeconvertertobesta ble, Mode10 mVIntroductionWhereListheoutputfilterind uctance, ,whereEsrisESRvalueoftheoutputcap, (R1+R2)onbothsidesoftheequation,whereR1, ,itisdiscoveredthatSrandthemagnitudeofth eoutputripplebotharetheoutputripplethatm atters, mode, , , July2007 RevisedDecember2007 AdaptiveConstantOn- time (D-CAP ) (10mV/Div)

4 400ns/DivLL(5V/Div)Shallow400ns/DivLL(5V /Div)Vout(10mV/Div)Deep sD-CAP formobileapplicationhasthestableswitchin gfrequencyatnormaloperation,smoothtransi tionbetweenskipmodetoPWMmode,fasttransie ntresponse, , , ,Current-modecontrol,fivedifferenttypes, usedwiththethreebasicclassesofpowerconve rters:Small-signalacandlarge-signaldccha racterization,stabilityrequirements,andi mplementationofpracticalcircuits, ,1985, modeoperationandanimplementationoftheOOA TM skipmode,TI sIntegratedPowerconference20058 AdaptiveConstantOn- time (D-CAP )ControlStudyinNotebookApplicationsSLVA2 81B July2007 RevisedDecember2007 SubmitDocumentationFeedbackIMPORTANTNOTI CET exasInstrumentsIncorporatedanditssubsidi aries(TI)

5 Reservetherighttomakecorrections,modific ations,enhancements,improvements, , , ,eitherexpressorimplied,isgrantedunderan yTIpatentright,copyright,maskworkright,o rotherTIintellectualpropertyrightrelatin gtoanycombination,machine, , ,conditions,limitations, (suchaslifesupport)whereafailureoftheTIp roductwouldreasonablybeexpectedtocausese verepersonalinjuryordeath, ,andacknowledgeandagreethattheyaresolely responsibleforalllegal,regulatoryandsafe ty-relatedrequirementsconcerningtheirpro ductsandanyuseofTIproductsinsuchsafety-c riticalapplications, , "enhancedplastic." 'srisk, ,iftheyuseanynon-designatedproductsinaut omotiveapplications, :TexasInstruments,PostOfficeBox655303,Da llas,Texas75265 Copyright 2007,TexasInstrumentsIncorporat