Designing Stable Compensation Networks for Single Phase Voltage Mode Buck Regulators

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1、DesigningStableCompensationNetworksfor®SinglePhaseVoltageModeBuckRegulatorsTechnicalBriefDecember2003TB417.1Author:DougMattinglyAssumptionsOutputFilterThisTechnicalBriefmakesthefollowingassumptions:Theoutputfilterconsistsoftheoutputinductorandalloftheoutputcapacitance.Iti

2、simportanttoincludetheDC1.Thepowersupplydesignerhasalreadydesignedtheresistance(DCR)oftheoutputinductorandthetotalpowerstageofthesinglephasebuckconverter.ThelastEquivalentSeriesResistance(ESR)oftheoutputcapacitorsteptothedesignisthecompensationnetwork.bank.Theinputtotheou

3、tputfilteristhePHASEnodeand2.Thedesignerhasatleastabasicunderstandingoftheoutputistheregulatoroutput.Figure3showsthecontrolsystemstheory.equivalentcircuitoftheoutputfilteranditstransferfunction.3.ThedesignerhasabasicunderstandingofBodeplots.LOIntroductionDCRVOUTSynchronou

4、sandnon-synchronousbuckregulatorshavePHASEthreebasicblocksthatcontributetotheclosedloopsystem.COTheseblocksconsistofthemodulator,theoutputfilter,andthecompensationnetworkwhichclosestheloopandESRstabilizesthesystem.ERRORAMPLIFIER+OUTPUTOUTPUT1sESRC+⋅⋅OUTMODULATORGAINFILTER

5、=----------------------------------------------------------------------------------------------------------------------------------------FILTER2_1++s⋅⋅()ESR+DCRCOUTs⋅⋅LOUTCOUTREFERENCEFIGURE3.THEOUTPUTFILTERCOMPENSATIONNETWORKThetransferfunctionfortheoutputfiltershowsthew

6、ellknowndoublepoleofanLCfilter.ItisimportanttonotethatFIGURE1.BASICBLOCKSOFTHEBUCKREGULATORtheESRofthecapacitorbankandtheDCRoftheinductorbothinfluencethedampingofthisresonantcircuit.ItisalsoModulatorimportanttonoticethesinglezerothatisafunctionoftheoutputcapacitanceandits

7、ESR.ThemodulatorisshowninFigure2.Theinputtothemodulatoristheoutputoftheerroramplifier,whichisusedOpenLoopSystemtocomparetheoutputtothereference.Figure4illustratestheopenloopsystemandpresentstheVINtransferfunction.DRIVEROSCPWMCOMPARATOR∆VOSCPHASELODCRVOUT-+OUTPUTOF-+ERRORA

8、MPLIFIERE/ACODRIVEROUTPUTESRFIGURE2.THEMODULATORTheoutputofthemodulatoristhePHASEnode.ThegainofV