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LDODCDCChargePump的原理比较与不同之处.ppt 43页
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LDODCDCChargePump的原理比较与不同之处
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*VoltageregulatorSimcomHardwareDept.2wangtaoAgendaVoltageregulatorpresentation: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)parewithstepdownbuckDC-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)LowvoltagedropLowcostRegulatorOverviewChargePumpTypesofChargePump
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