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
TPS786xx
1
µ
F
BoardLayoutRecommendationtoImprove
ExternalCapacitorRequirements
RegulatorMounting
tps78601,tps78618
tps78625,tps78628
tps78630,tps78633
SLVS389D–SEPTEMBER2002–REVISEDOCTOBER2004
flowoutofthenrpinmustbeataminimum,
thetps786xxfamilyoflow-落后(ldo)regulators
becauseanyleakagecurrentcreatesanIRdrop
hasbeenoptimizedforuseinnoise-sensitiveequip-
acrosstheinternalresistor,thuscreatinganoutput
ment.thedevicefeaturesextremelylowdropout
错误.因此,thebypasscapacitormusthave
电压,highpsrr,ultralowoutputnoise,低
minimalleakagecurrent.thebypasscapacitor
quiescentcurrent(265µatypically),andenableinput
shouldbenomorethan0.1-µftoensurethatitisfully
toreducesupplycurrentstolessthan1µAwhenthe
chargedduringthequickstarttimeprovidedbythe
regulatoristurnedoff.
internalswitchshowninthefunctionalblockdiagram.
atypicalapplicationcircuitisshowninfigure24.
forexample,thetps78630exhibitsonly48µv
RMS
ofoutputvoltagenoiseusinga0.1-µfceramic
bypasscapacitoranda10-µfceramicoutputcapaci-
tor.notethattheoutputstartsupslowerasthe
bypasscapacitanceincreasesduetotheRCtime
constantatthebypasspinthatiscreatedbythe
internal250-k
Ω
resistorandexternalcapacitor.
figure24.typicalapplicationcircuit
PSRRandNoisePerformance
toimproveacmeasurementslikepsrr,输出
噪音,andtransientresponse,itisrecommendedthat
a2.2-µforlargerceramicinputbypasscapacitor,
theboardbedesignedwithseparategroundplanes
connectedbetweenINandGNDandlocatedcloseto
forV
在
andV
输出
,witheachgroundplaneconnected
thetps786xx,isrequiredforstabilityandimproves
onlyatthegroundpinofthedevice.inaddition,这
transientresponse,noiserejection,andripplerejec-
groundconnectionforthebypasscapacitorshould
tion.ahigher-valueinputcapacitormaybenecessary
connectdirectlytothegroundpinofthedevice.
iflarge,快-上升-timeloadtransientsareanticipated
andthedeviceislocatedseveralinchesfromthe
powersource.
likemostlowdropoutregulators,thetps786xx
thetabofthesot223-6packageiselectrically
requiresanoutputcapacitorconnectedbetweenOUT
connectedtoground.forbestthermalperformance,
andgndtostabilizetheinternalcontrolloop.这
thetabofthesurface-mountversionshouldbe
minimumrecommendedcapacitanceis1µf.any1
soldereddirectlytoacircuit-boardcopperarea.
µforlargerceramiccapacitorissuitable.
increasingthecopperareaimprovesheatdissipation.
Theinternalvoltagereferenceisakeysourceof
Solderpadfootprintrecommendationsforthedevices
noiseinanldoregulator.thetps786xxhasannr
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
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