根据datasheet P21 输入电容和输出电容的说明再改进测试一下。
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Input Capacitor
Atleast a20μFinput capacitoris recommended to improve transient behaviorofthe regulator andEMIbehavior
ofthe total powersupplycircuit.Aceramiccapacitorplacedascloseaspossibleto the VINandPGNDpinsof
the IC is recommended.
OutputCapacitor
Forthe outputcapacitor,useofasmallceramiccapacitorsplacedascloseaspossibleto the VOUTandPGND
pinsofthe IC is recommended. If, for anyreason, the applicationrequires the useoflarge capacitorswhichcan
not beplacedclose to the IC, useasmaller ceramiccapacitor in parallelto the large capacitor. Thesmall
capacitor shouldbeplacedascloseaspossibleto the VOUTandPGNDpinsofthe IC. Therecommended
typical outputcapacitorvalueis 66µFwithavarianceasoutlinedin Table2.
Thereis alsonoupperlimit for the outputcapacitancevalue.Largercapacitorswillcauselower outputvoltage
ripple aswellaslower outputvoltagedropduringload transients.
Whenchoosing input and output capacitors, it needs to be kept in mind,that the value of capacitance
experiencessignificantlosses from their rated valuedependingonthe operatingtemperature andthe operating
DCvoltage.It's notuncommonfor asmallsurfacemountceramiccapacitorto lose 50%andmoreofit's rated
capacitance. Forthis reason, it is important to usealarger value ofcapacitance or acapacitor withhigher
voltageratingin orderto ensurethe required capacitanceatthe full operatingvoltage.
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