www.德州仪器.com
BoardLayoutRecommendationtoImprove
TransientResponse
InternalCurrentLimit
关闭
(fixedVoltage 版本)
dV
dt
V
输出
C
输出
80k
R
加载
(4)
DropoutVoltage
(adjustable voltage 版本)
dV
dt
V
输出
C
输出
80k
(
R
1
R
2
)
R
加载
(5)
TPS736xx
SBVS038K–SEPTEMBER2003–REVISEDSEPTEMBER2005
thisnoisereductioneffectisshownasrmsnoiseforlargestepchangesinloadcurrent,thetps736xx
VoltagevsC
NR
inthetypicalcharacteristicssection.requiresalargervoltagedropfromv
在
toV
输出
至
avoiddegradedtransientresponse.theboundaryof
TheTPS73601adjustableversiondoesnothavethe
thistransientdropoutregionisapproximatelytwice
噪音-reductionpinavailable.不管怎样,connectinga
thedcdropout.valuesofv
在
-v
输出
abovethisline
feedbackcapacitor,c
FB
,fromtheoutputtothefb
insurenormaltransientresponse.
pinwillreduceoutputnoiseandimproveloadtransi-
entperformance.operatinginthetransientdropoutregioncancause
anincreaseinrecoverytime.thetimerequiredto
TheTPS736xxusesaninternalchargepumpto
recoverfromaloadtransientisafunctionofthe
developaninternalsupplyvoltagesufficienttodrive
magnitudeofthechangeinloadcurrentrate,therate
thegateoftheNMOSpasselementaboveV
输出
.这
ofchangeinloadcurrent,andtheavailablehead-
chargepumpgenerates~250µVofswitchingnoiseat
房间(v
在
toV
输出
voltagedrop).underworst-情况
~4mhz;不管怎样,承担-pumpnoisecontributionis
conditions[full-scaleinstantaneousloadchangewith
negligibleattheoutputoftheregulatorformost
(v
在
-v
输出
)closetodcdropoutlevels],thetps736xx
valuesofI
输出
andC
输出
.
cantakeacoupleofhundredmicrosecondstoreturn
tothespecifiedregulationaccuracy.
PSRRandNoisePerformance
toimproveacperformancesuchaspsrr,输出
thelowopen-loopoutputimpedanceprovidedbythe
噪音,andtransientresponse,itisrecommendedthat
nmospasselementinavoltagefollowerconfigur-
theboardbedesignedwithseparategroundplanes
ationallowsoperationwithoutanoutputcapacitorfor
forV
在
andV
输出
,witheachgroundplaneconnected
manyapplications.aswithanyregulator,theaddition
onlyatthegndpinofthedevice.inaddition,这
ofacapacitor(nominalvalue1µf)fromtheoutputpin
groundconnectionforthebypasscapacitorshould
togroundwillreduceundershootmagnitudebut
connectdirectlytothegndpinofthedevice.
increaseduration.intheadjustableversion,这
additionofacapacitor,c
FB
,fromtheoutputtothe
adjustpinwillalsoimprovethetransientresponse.
TheTPS736xxinternalcurrentlimithelpsprotectthe
thetps736xxdoesnothaveactivepull-downwhen
regulatorduringfaultconditions.foldbackhelpsto
theoutputisover-电压.thisallowsapplications
protecttheregulatorfromdamageduringoutput
thatconnecthighervoltagesources,suchasalter-
短的-circuitconditionsbyreducingcurrentlimitwhen
natepowersupplies,totheoutput.thisalsoresults
V
输出
dropsbelow0.5v.看Figure11intheTypical
inanoutputovershootofseveralpercentifload
CharacteristicssectionforagraphofI
输出
vsV
输出
.
currentquicklydropstozerowhenacapacitoris
connectedtotheoutput.thedurationofovershoot
canbereducedbyaddingaloadresistor.这
overshootdecaysataratedeterminedbyoutput
TheEnablepinisactivehighandiscompatiblewith
capacitorC
输出
andtheinternal/externalloadresist-
standardttl-cmoslevels.v
EN
below0.5v(最大值)
ance.therateofdecayisgivenby:
turnstheregulatoroffanddropsthegroundpin
currenttoapproximately10na.whenshutdowncapa-
bilityisnotrequired,theenablepincanbeconnected
toV
在
.whenapull-upresistorisused,andoperation
downto1.8visrequired,usepull-upresistorvalues
below50k
Ω
.
TheTPS736xxusesanNMOSpasstransistorto
achieveextremelylowdropout.当(v
在
-v
输出
)是
lessthanthedropoutvoltage(v
做
),thenmospass
deviceisinitslinearregionofoperationandthe
输入-至-outputresistanceisther
ds-在
oftheNMOS
passelement.
12
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