www.德州仪器.com
APPLICATIONINFORMATION
BoardLayoutRecommendationtoImprove
GNDEN NR
在 输出
V
在
V
输出
0.01
µ
F
TPS796xx
2.2
µ
F 1
µ
F
ExternalCapacitorRequirements
RegulatorMounting
ProgrammingtheTPS79601AdjustableLDO
V
O
V
REF
1
R1
R2
(1)
tps79601,tps79618,tps79625
tps79628,tps79630,tps79633
SLVS351D–SEPTEMBER2002–REVISEDOCTOBER2004
thetps796xxfamilyoflow-落后(ldo)regulatorsforexample,thetps79630exhibits40µv
RMS
的
hasbeenoptimizedforuseinnoise-sensitiveequip-outputvoltagenoiseusinga0.1-µfceramicbypass
ment.thedevicefeaturesextremelylowdropoutcapacitoranda10-µfceramicoutputcapacitor.便条
电压,highpsrr,ultralowoutputnoise,lowthattheoutputstartsupslowerasthebypass
quiescentcurrent(265µatypically),andenableinputcapacitanceincreasesduetotherctimeconstantat
toreducesupplycurrentstolessthan1µawhenthethebypasspinthatiscreatedbytheinternal250-k
Ω
regulatoristurnedoff.resistorandexternalcapacitor.
atypicalapplicationcircuitisshowninfigure22.
PSRRandNoisePerformance
toimproveacmeasurementslikepsrr,输出
噪音,andtransientresponse,itisrecommendedthat
theboardbedesignedwithseparategroundplanes
forV
在
andV
输出
,witheachgroundplaneconnected
onlyatthegroundpinofthedevice.inaddition,这
figure22.typicalapplicationcircuit
groundconnectionforthebypasscapacitorshould
connectdirectlytothegroundpinofthedevice.
althoughnotrequired,itisgoodanalogdesign
thetabofthesot223-6packageiselectrically
practicetoplacea0.1-µf—2.2-µfcapacitornear
connectedtoground.forbestthermalperformance,
theinputoftheregulatortocounteractreactiveinput
thetabofthesurface-mountversionshouldbe
来源.a2.2-µforlargerceramicinputbypass
soldereddirectlytoacircuit-boardcopperarea.
电容,connectedbetweeninandgndand
increasingthecopperareaimprovesheatdissipation.
locatedclosetothetps796xx,isrequiredforstability
andimprovestransientresponse,noiserejection,和
Solderpadfootprintrecommendationsforthedevices
ripplerejection.ahigher-valueinputcapacitormaybe
arepresentedinanapplicationbulletin
SolderPad
necessaryiflarge,快-上升-timeloadtransientsare
recommendationsforsurface-mountdevices
,litera-
anticipatedandthedeviceislocatedseveralinches
turenumberab-132,availablefordownloadfromthe
fromthepowersource.
tiwebsite(www.德州仪器.com).
likemostlowdropoutregulators,thetps796xx
requiresanoutputcapacitorconnectedbetweenOUT
调整器
andgndtostabilizetheinternalcontrolloop.这
minimumrecommendedcapacitanceis1µf.任何
TheoutputvoltageoftheTPS79601adjustable
1µforlargerceramiccapacitorissuitable.
regulatorisprogrammedusinganexternalresistor
dividerasshowninfigure28.theoutputvoltageis
Theinternalvoltagereferenceisakeysourceof
calculatedusingequation1:
noiseinanldoregulator.thetps796xxhasannr
pinwhichisconnectedtothevoltagereference
througha250-k
Ω
internalresistor.the250-k
Ω
internalresistor,inconjunctionwithanexternalby-
在哪里:
passcapacitorconnectedtothenrpin,createsa
低-passfiltertoreducethevoltagereferencenoise
•
V
REF
=1.2246vtyp(theinternalreference
和,因此,thenoiseattheregulatoroutput.在
电压)
orderfortheregulatortooperateproperly,thecurrent
resistorsr1andr2shouldbechosenforapproxi-
flowoutofthenrpinmustbeataminimum,
mately40-µadividercurrent.lowervalueresistors
becauseanyleakagecurrentcreatesanIRdrop
canbeusedforimprovednoiseperformance,butthe
acrosstheinternalresistor,thuscreatinganoutput
devicewastesmorepower.highervaluesshouldbe
错误.因此,thebypasscapacitormusthave
避免,asleakagecurrentatfbincreasesthe
minimalleakagecurrent.thebypasscapacitor
outputvoltageerror.
shouldbenomorethan0.1-µfinordertoensurethat
itisfullychargedduringthequickstarttimeprovided
bytheinternalswitchshowninthefunctionalblock
图解.
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