电源设计技术(线性电源及buck电源设计基础)ppt课件.ppt

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1、EDPPowerSolutionsAgendaLinearRegulatorsAnLDOPrimerElectricaldesignThermalconsiderationsLayouthintsSwitchersTopologiesMeetingSpecificationsLayoutconstraints9/16/982EDPPowerSolutionsAnLDOPrimerTypesOfLowDropoutRegulatorNPNNPNwithdualinputsPNPNMOSPMOSNPNBasedLDODropout=1.3Vmax.PNPVCE(SAT)+NPNVB

2、ELowquiescentcurrentNearlyalldrivecurrentflowsintoloadIdealfor5Vto3.3VAminimumloadcurrentisrequiredforregulationCanbemetusingtheresistorfeedbackchainNPNWithDualInputsDropout=0.6~0.8Vmax.NPNVCE(SAT)LowquiescentcurrentNearlyalldrivecurrentflowsintoloadIdealfor3.3Vto2.5VNeedsasecond,higherinput

3、fordriveAminimumloadcurrentisrequiredforregulationCanbemetusingtheresistorfeedbackchainPNPBasedLDODropout=0.2~0.3VPNPVCE(SAT)IdealforbatterypoweredsystemswhereheadroomislowHighquiescent(groundpin)currentindropoutN-ChannelMOSFETLowdropoutIOxRDS(ON)VerylowquiescentcurrentNearlyindependentofout

4、putcurrentsinceFETisvoltagedrivenSlowertransientresponsetimeduetochargepumpFasteroscillatorhelpsDualinputversionremovesneedforchargepumpP-ChannelMOSFETLowdropoutIOxRDS(ON)VerylowquiescentcurrentNearlyindependentofoutputcurrentsinceFETisvoltagedrivenNochargepumpresponsetimeissuesLimitedVGSlim

5、itsRDS(ON),hencecurrentratingElectricalDesignLDOorSwitcher?ComponentSelectionSettingtheoutputvoltageSelectingoutputcapacitanceSelectinginputcapacitanceBypasscapacitanceanyone?LDOProsandConsLDOAdvantagesNoswitchingnoiseSimpletouseLowcostLDODisadvantagesLowefficiency=VOUT/VINCarefulthermaldesi

6、gnrequiredAthigherpowerlevels,heatsinkstakeupspaceandaddtocostHeateffectonsystemSettingVOUT“Floating”ReferencesIREF(typ.~50µA)termusuallynegligibleCanselectR1suchthat“Grounded”References1%metalfilmresistorsrecommendedSelectingCOUTAminimumcapacitanceisusuallyrequiredbytheLDOforstabilityMinimu

7、mcapacitancevalueandmaximumESRforapplicationisdefinedbythemaximumallowablechangeinoutputvoltagewhere:VINSTisdeterminedbytheESRandESLofthecapacitor:Usually,LESLtermcanbeignoredSelectingCOUTVDROOPisdeterminedbythebulkcapacitance:t=LDOresponsetime,usu