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APPLICATIONINFORMATION
V
在
V
输出
GNDEN NR
在 输出
V
在
V
输出
0.1
µ
F
0.01
µ
F
2.2
µ
F
TPS730xx
ExternalCapacitorRequirements
BoardLayoutRecommendationtoImprovePSRRandNoisePerformance
tps73001,tps73018
TPS73025
tps73030,tps73033
SBVS054A–NOVEMBER2004–REVISEDNOVEMBER2004
thetps730xxfamilyoflow-落后(ldo)regulatorshasbeenoptimizedforuseinnoise-敏感的
电池-operatedequipment.thedevicefeaturesextremelylowdropoutvoltages,highpsrr,ultralowoutput
噪音,lowquiescentcurrent(170µatypically),andenable-inputtoreducesupplycurrentstolessthan1µa
whentheregulatoristurnedoff.
atypicalapplicationcircuitisshowninfigure16.
figure16.typicalapplicationcircuit
a0.1-µforlargerceramicinputbypasscapacitor,connectedbetweeninandgndandlocatedclosetothe
tps730xx,isrequiredforstabilityandimprovestransientresponse,noiserejection,andripplerejection.一个
高等级的-valueinputcapacitormaybenecessaryiflarge,快-上升-timeloadtransientsareanticipatedorthedevice
islocatedseveralinchesfromthepowersource.
likemostlowdropoutregulators,thetps730xxrequiresanoutputcapacitorconnectedbetweenoutandgnd
tostabilizetheinternalcontrolloop.theminimumrecommendedcapacitanceis2.2µf.any2.2-µforlarger
ceramiccapacitorissuitable,providedthecapacitancedoesnotvarysignificantlyovertemperature.ifload
currentisnotexpectedtoexceed100ma,a1.0-µfceramiccapacitorcanbeused.
theinternalvoltagereferenceisakeysourceofnoiseinanldoregulator.thetps730xxhasannrpinwhich
isconnectedtothevoltagereferencethrougha250-k
Ω
internalresistor.the250-k
Ω
internalresistor,在
conjunctionwithanexternalbypasscapacitorconnectedtothenrpin,createsalowpassfiltertoreducethe
voltagereferencenoiseand,因此,thenoiseattheregulatoroutput.inorderfortheregulatortooperate
合适的,thecurrentflowoutofthenrpinmustbeataminimum,becauseanyleakagecurrentcreatesanir
dropacrosstheinternalresistorthuscreatinganoutputerror.因此,thebypasscapacitormusthave
minimalleakagecurrent.thebypasscapacitorshouldbenomorethan0.1-µftoensurethatitisfullycharged
duringthequickstarttimeprovidedbytheinternalswitchshownintheFunctionalBlockDiagrams
asanexample,thetps73018exhibitsonly23µv
RMS
ofoutputvoltagenoiseusinga0.01-µfceramicbypass
capacitoranda2.2-µfceramicoutputcapacitor.notethattheoutputstartsupslowerasthebypasscapacitance
increasesduetotherctimeconstantatthenrpinthatiscreatedbytheinternal250-k
Ω
resistorandexternal
电容.
toimproveacmeasurementslikepsrr,outputnoise,andtransientresponse,itisrecommendedthattheboard
bedesignedwithseparategroundplanesforV
在
andV
输出
,witheachgroundplaneconnectedonlyatthegnd
pinofthedevice.inaddition,thegroundconnectionforthebypasscapacitorshouldconnectdirectlytothegnd
pinofthedevice.
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