www.德州仪器.com
APPLICATIONINFORMATION
GNDEN NR
在 输出
V
在
V
输出
0.01
µ
F
2.2
µ
F
1
µ
F
TPS795xx
BoardLayoutRecommendationtoImprove
ExternalCapacitorRequirements
RegulatorMounting
tps79501,tps79516
tps79518,tps79525
tps79530,tps79533
SLVS350B–OCTOBER2002–REVISEDOCTOBER2004
becauseanyleakagecurrentcreatesanIRdrop
thetps795xxfamilyoflow-落后(ldo)regulators
acrosstheinternalresistorthuscreatinganoutput
hasbeenoptimizedforuseinnoise-sensitiveequip-
错误.因此,thebypasscapacitormusthave
ment.thedevicefeaturesextremelylowdropout
minimalleakagecurrent.thebypasscapacitor
电压,highpsrr,ultralowoutputnoise,低
shouldbenomorethan0.1-µfinordertoensurethat
quiescentcurrent(265µatypically),andenableinput
itisfullychargedduringthequickstarttimeprovided
toreducesupplycurrentstolessthan1µAwhenthe
bytheinternalswitchshowninthefunctionalblock
regulatoristurnedoff.
图解.
atypicalapplicationcircuitisshowninfigure23.
forexample,thetps79530exhibitsonly33µv
RMS
ofoutputvoltagenoiseusinga0.1-µfceramic
bypasscapacitoranda10-µfceramicoutputcapaci-
tor.notethattheoutputstartsupslowerasthe
bypasscapacitanceincreasesduetotheRCtime
constantatthebypasspinthatiscreatedbythe
internal250-k
Ω
resistorandexternalcapacitor.
figure23.typicalapplicationcircuit
PSRRandNoisePerformance
toimproveacmeasurementslikepsrr,输出
a1-µforlargerceramicinputbypasscapacitor,
噪音,andtransientresponse,itisrecommendedthat
connectedbetweenINandGNDandlocatedcloseto
theboardbedesignedwithseparategroundplanes
thetps795xx,isrequiredforstabilityandimproves
forV
在
andV
输出
,witheachgroundplaneconnected
transientresponse,noiserejection,andripplerejec-
onlyatthegroundpinofthedevice.inaddition,这
tion.ahigher-valueinputcapacitormaybenecessary
groundconnectionforthebypasscapacitorshould
iflarge,快-上升-timeloadtransientsareanticipated
connectdirectlytothegroundpinofthedevice.
andthedeviceislocatedseveralinchesfromthe
powersource.
likemostlowdropoutregulators,thetps795xx
thetabofthesot223-6packageiselectrically
requiresanoutputcapacitorconnectedbetweenOUT
connectedtoground.forbestthermalperformance,
andgndtostabilizetheinternalcontrolloop.这
thetabofthesurface-mountversionshouldbe
minimumrecommendedcapacitanceis1µf.任何
soldereddirectlytoacircuit-boardcopperarea.
1µforlargerceramiccapacitorissuitable.
increasingthecopperareaimprovesheatdissipation.
Theinternalvoltagereferenceisakeysourceof
Solderpadfootprintrecommendationsforthedevices
noiseinanldoregulator.thetps795xxhasannr
arepresentedinanapplicationbulletin
SolderPad
pinwhichisconnectedtothevoltagereference
recommendationsforsurface-mountdevices
,litera-
througha250-k
Ω
internalresistor.the250-k
Ω
turenumberab-132,availablefromthetiwebsite
internalresistor,inconjunctionwithanexternalby-
(www.德州仪器.com).
passcapacitorconnectedtothenrpin,createsa
lowpassfiltertoreducethevoltagereferencenoise
和,因此,thenoiseattheregulatoroutput.在
orderfortheregulatortooperateproperly,thecurrent
flowoutofthenrpinmustbeataminimum,
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