LDO-DCDC-Charge-Pump的原理比較與不同之處

VoltageregulatorSimcomHardwareDept.2

wangtaoAgendaVoltageregulatorpresentation:AC-ACDC-ACDC-DCAgendaDC-DCVoltageregulatorpresentation:LDOChargepump(inductorlessDC-DC)DC-DC(inductor)LDOLDO(LowDropout)LDOisalinearregulatorDropoutvoltageoutputvoltagewithin100mV,(Vin–Vout)minLDOLDOWorkingprinciple:ThevoltagedividedbyresistorsR1&R2iscomparedwiththeinternalreferencevoltagebytheerroramplifierTheMOSFET,whichisconnectedtotheVoutpin,isthendrivenbythesubsequentoutputsignal.TheoutputvoltageattheVoutpiniscontrolled&stabilizedbyasystemofnegativefeedback.LDOparameters?InputVoltageTheminimumVinmustbelargerthanVout+VDO,independentfromtheminimumvaluegivenintheselectiontable.?EfficiencyByneglectingthequiescentcurrent(Iq)oftheLDO,efficiencycanbecalculatedasVout/Vin.LDOparameters?PowerDissipationPD=(Vin–Vout)xIout;PDislimitedbypackage.ComparewithstepdownbuckDC-DC,forhigherpowerdissipationorrequirementsforhigherefficiency,recommendbuck.?CapacitorRequirementsTheoutputcapacitorandespeciallyEquivalentSeriesResistance(ESR)arecriticalforstability.?NoiseandPSRRSelectanLDOwithhighpowersupplyrejectionratio(PSRR)fornoiseimmunityfromtheinputsupplyandlowoutputnoise.SomeLDOhaveabypass(BP)pinforaddingcapacitancetolowertheoutputnoise.LDOparametersCeramicCapacitorEquivalentCircuitEquivalentSeriesResistance(ESR)isacriticalfactorincircuitperformanceCapacitorImpedanceisafunctionof:CapValue,ESRandFrequencyLDOparametersThingstoknowaboutCeramicCaps:ESRisafunctionof:PhysicalsizeLargercasesizecapshavelowerESRMaterialTypeX7R–Best(lowestESR)X5R–GoodY5V–Lowcost(highestESR)Capacitancevs.Frequency:Capacitancevaluebecomessmallerasfrequencyincreases(impedancedrops)AgainmaterialtypehasaneffectLDOparametersX7RMaterialMLCCLowerESRLowerimpedanceBetterCapacitancevs.FrequencyGoodTemp.Tolerance(+/-10%)Y5VMaterialMLCCHigherESRHigherimpedancePoorCapacitancevs.FrequencyPoorTemp.Tolerance(+20/-80%)LDOselection:LOWnoise,HIGHPSRNoenoughPCBarea(inductorless)LowvoltagedropLowcostRegulatorOverviewChargePumpTypesofChargePumpDevices:TypesofChargepumpdevicesareavailableindifferenttopologies:VoltageDoubling(2X)ChargePumpsVout=2xVinFractionalChargePumpsVout=NxVin,whereN=devicemultiplicationExample:Vout=1.5xVinRegulatedOutputChargePumpsCanbe2x,3x,Fractional,etc.VoltageDoubleChargePumpWorkingprinciple:Voltagedoublechargepumpblockdiagram(Vout=2xVin)ChargePumpPhaseCycle1:ChargeCFLYChargePumpPhaseCycle2:BootstrapCFLYtotheOutputVoltageDoubleChargePumpEquivalentCircuitforPhaseCycle1:EquivalentCircuitforPhaseCycle2:FractionalChargePumpWorkingprinciple:FractionalChargePumps:Fractionalchargepumpsofferatechniquetomultiplyaninputvoltagebyanon-integermultiplicationfactorFractionalchargepumpscanhaveefficiencyadvantagesinlowoutputvoltageapplicationsEquivalentCircuitforPhaseCycle1:EquivalentCircuitforPhaseCycle2:FractionChargePumpWorks:Operateswith2switchingcyclephases(sameasavoltagedoublingchargepump)Two“Flying”capacitorsareused:InthefirstswitchingcycleCFLY1andCFLY2areconnectedinseriesandplacedacrossVin,whicheffectsavoltagedivideratVc=Vin/2foreach“Fly”capacitor.InthesecondswitchingcycleCFLY1andCFLY2areconnectedinparallel,thenswitchedtobeinseriesbetweenVinandVout.Vout=Vin+Vin/2=1.5xVinFractionalChargePumpRegulatedChargePumpWorkingprinciple:RegulatedChargePumps:Regulatedchargepumpsarevoltagedoubling,triplingorfractionalchargepumpswithanoutputvoltageregulationsystemandfeedbackcontrol.Regulatedchargepumpscanprovideastableoutputvoltagefromavariedinputsupply,whichisidealforbatteryoperateddevices.ChargePumpEfficiencyPrimaryitemswhicheffectefficiency:RDS(ON)oftheMOSFETswitchingdevicesI2RLoss–LowerRDSspecsarebetterOperatingquiescentcurrentVinversusVoutforagivenchargepumptopology-ThisappliestoregulatedchargepumpsTypesofexternalcapacitorsused-Cin,CoutandCflyChargePumpEfficiencyEfficiencyofRegulatedChargePumps:RegulatedVoltageDoublingChargePumpsFixedoutputvoltagelevelInputvoltagemayvarywithinthedeviceoperatingrangeTheinputvoltageisdoubled,thenregulateddowntothedesiredoutputvoltage.TheoreticalEfficiency==VOUT/2VINExample:VIN=2.8V,VOUT=3.3V,=58.9%Example:VIN=3V,VOUT=4.5V,=75%ChargePumpEfficiencyEfficiencyofFractionalChargePumps:RegulatedFractionalChargePumpsFixedoutputvoltagelevelInputvoltagemayvarywithinthedeviceoperatingrangeFractionalchargepumpshaveanadvantageinlowvoltageapplicationssincetheInputtoOutputdifferencevoltagetoberegulatedissmall.TheoreticalEfficiency==VOUT/1.5VINExample:VIN=2.8V,VOUT=3.3V,=78.6%Example:VIN=3V,VOUT=4.5V,100%ExternalcomponentselectionExternalComponentSelection:Chargepumpdevicestypicallyrequire3to4externalcapacitorsdependinguponcircuittopology.TheCIN/COUTtoCFLYratiocanrangefrom1:1to10:1CapacitorvalueandpropertiesarecriticaltogoodchargepumpperformanceImportantCapacitorCharacteristics:CapacitorvalueDielectricmaterialtypePhysicalsizeCapacitorequivalentseriesresistance(ESR)Capacitorselection:CeramicCapacitorsaretypicallythebestchoiceCeramiccapacitorsarenon-polarizedandhavelowESRcharacteristics,typically<100m

CeramicCapacitorESR:CapacitorESRhasadramaticeffectonoutputrippleESRcanvarydependingcapacitortype,valueandcasesize.X7RDielectricisthebest(highercost)X5RDielectricisgoodY5VDielectricispoor(lowercost)TantalumandAluminumElectrolyticCapacitorsThesetypesofcapacitorsmaybeusedwithchargepumpsforCinandCoutattheexpenseofperformanceBothhavehighESRcharacteristicsOutputrippleandefficiencywillbecompromisedCFLYmustbeanon-polarizedcapacitor(bi-directionalcurrentflow)ExternalcomponentselectionChargepump–outputrippleOutputRippleCharacteristics:Outputrippleissignificantlyeffectedbytheexternalcapacitorvalue.ThefollowingplotsareexamplesmeasuredwithanAAT3111showinghowcapacitorvaluecaneffectoutputripple.AAT3111:VIN=3.0V,VOUT=5.0V,ILOAD=50mA0805Size,X7RCeramicCIN=COUT=2.2uFCFLY=0.22uFVripple=60mVp-p0805Size,X7RCeramicCIN=COUT=4.7uFCFLY=0.47uFVripple=45mVp-p0805Size,X7RCeramicCIN=COUT=10uFCFLY=1uFVripple=30mVp-pChargepump–outputrippleOutputRippleCharacteristics:Outputrippleissignificantlyeffectedbytheexternalcapacitormaterialtype.ThefollowingexamplesweremeasuredwithanAAT3110showinghowequalvalueandsizecapacitorsofdifferentmaterialtypescaneffectoutputripple.AAT3110:VIN=3.0V,VOUT=5.0V,ILOAD=50mA0805Size,Y5VCeramicCIN=COUT=10uFCFLY=1uFVripple=90mVp-p!!!0805Size,X7RCeramicCIN=COUT=10uFCFLY=1uFVripple=35mVp-pDC-DCthreebasicswitchingtopologiesincommonTypesofDC-DCdevicesareavailableinthreetopologies:BUCKStep-downpowerstage.Powersupplydesignerschoosethebuckpowerstage.therequiredoutputvoltageisalwayslowerthantheinputvoltageBOOSTstep-uppowerstage.Powersupplydesignerschoosetheboostpowerstage.therequiredoutputvoltageisalwayshigherthantheinputvoltageBUCK/BOOSTstep-up/downpowerstage.Powersupplydesignerschoosethebuck-boostpowerstage.theoutputvoltageisinvertedfromtheinputvoltage,andtheoutputvoltagecanbeeitherhigherorlowerthantheinputvoltage.StepDown“Buck”ConverterStepUP“Boost”ConverterStepUp/StepDown“Buck-Boost”ConverterDC-DCDC-DCPWMControlSignalDetailsDCsteadystateassumesVOUTandVINareconstantSteadystatedictatesthattheaverageinductorvoltagemustbezero(volt-secbalance)TheinductorDCcurrentisequaltotheloadcurrent…noDCcurrentintotheoutputcap…constantoutputvoltage

DC-DCBasicStep-Down“Buck”DC/DCConverter

SimpleControl80-90%efficiencyatfullloadSwitchingfrequency30kHz-4MHzLightloadefficiencyimprovementwithburstmode,frequencyshiftorpulseskippingDC-DCPWMSwitchingControl:OutputVoltageistheaverageofthevoltageappliedtotheoutputLCfilterDC-DCSynchronousStep-DownDC/DCConversionMoreefficientthanaconventionalBuckconverterEliminatestheexternalSchotkyDiodeRequired“dead-time”breakbeforemakeswitchingtolimitshoot-thrucurrentandimproveefficiencyMadepossiblebyuseofCMOSprocesstechnologyLightLoadEfficiencyImprovementsPulseskippingorBurstModeatlightloadtoreduceswitchinglossesControlMosfetSynchronousMosfetDC-DCSynchronousSwitching“Dead-Time”Whatisit?TimewhenbothcontrolandsynchronousswitchesareoffAdvantageEliminatesMosfetshoot-thrucurrentandassociatedlossesReducesswitchinglossesassociatedwiththeturnonofthesynchronousswitch(VDSiszerowhenVGSisapplied)DisadvantageDiodebodylossesaregreaterthanMosfetRDS(ON)lossesforthesamecurrentduringthedeadtime.SolutionDesignsynchronousconverterswithgoodbreak-before-switchingUseaveryhighswitchingfrequencySub-micronCMOSandBCDprocessallowthesolutiontobepossibleDC-DCSynchronousSwitchingStatesDC-DCSoft-StartisVeryImportantSwitchersReducesIn-rushcurrentsduringstart-upLimitssupplyrailvoltagesagatstart-upSoft-Startswitcherturn-onresponseSwitcherturn-onresponsewithoutsoft-startDC-DCTypicalIOUTCurrentLimitResponseILIMITat1.3AforVOUT=1.5VILIMITat1.2AforVOUT=3.3VDC-DCHighvsLowSwitchingFrequencyHighswitchingfrequencies:Typicalswitchingfrequenciesabove800kHzAllowfortheuseofsmallexternalcomponentsOutputinductorsandcapacitorsPermittheuseofswitchingconvertersinRFapplicationsHighswitchingfrequenciesarelesslikelytointerferewithbasebandsystemsGoodTransientresponseLowerswitchingrippleLowswitchingfrequencies:Typicalswitchingfrequenciesfrom20kHzto800kHzPoortransientresponseLargeexternalcomponentsHighswitchingrippleandnoiseLowcost/performanceswitchingconvertsExternalcomponentselectionExternalComponentSelection: GoodperformanceisdependantupontherightexternalcomponentselectionOutputCapacitorsCeramicCapacitorsAppliestobothSwitchingandLinear(LDO)RegulatorsOutputInductorInductorsWireWoundMultilayerChipDiodeExternalcomponentselectionCapacitorselection:TheCapacitorshouldbelowESRMinimizedswitchingnoiseandrippleForbesttransientresponseDifferentMaterialTypesEffectperformanceX7R,X5RandY5VaremostcommonOnemustbalancecircuitperformancevs.sizeandcostlimitationsExternalcomponentselectionInductorselection:TheinductorshouldbelowESRForbestpowerconversionefficiencyMinimizedswitchingnoiseandrippleLowHeightprofileIfusedinportableproductsMagneticshieldedIfusedinwireless/RFapplicationsOnemustbalancecircuitperformancevs.sizeandcostlimitationsWireWoundFerriteinductorWireWoundFerriteinductorsaresuperior