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ID:58730492
大小:1.02 MB
页数:62页
时间:2020-10-04
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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
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