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DROPOUTVOLTAGE
BOARDLAYOUTRECOMMENDATIONTO
TRANSIENTRESPONSE
INTERNALCURRENTLIMIT
关闭
dV
dt
V
输出
C
输出
80k
(4)
tps73101,tps73115,tps73118
tps73125,tps73130,tps73132
tps73133,tps73150
SBVS034E–SEPTEMBER2003–REVISEDSEPTEMBER2004
Thisnoisereductioneffectisshownas
RMSNoise
VoltagevsC
NR
inthetypicalcharacteristicssection.
TheTPS731xxusesanNMOSpasstransistorto
thetps73101adjustableversiondoesnothavetheachieveextremelylowdropout.当(v
在
-v
输出
)是
噪音-reductionpinavailable.不管怎样,connectingalessthanthedropoutvoltage(v
做
),thenmospass
feedbackcapacitor,c
FB
,fromtheoutputtothefbpindeviceisinitslinearregionofoperationandthe
willreduceoutputnoiseandimproveloadtransientinput-至-outputresistanceisther
ds-在
oftheNMOS
效能.passelement.
thetps731xxusesaninternalchargepumptoforlargestepchangesinloadcurrent,thetps731xx
developaninternalsupplyvoltagesufficienttodriverequiresalargervoltagedropacrossittoavoid
thegateoftheNMOSpasselementaboveV
输出
.thedegradedtransientresponse.theboundaryofthis
chargepumpgenerates~250µVofswitchingnoiseattransientdropoutregionisapproximatelytwicethedc
~4mhz;不管怎样,承担-pumpnoisecontributionisdropout.valuesofv
在
-v
输出
abovethislineinsure
negligibleattheoutputoftheregulatorformostnormaltransientresponse.
valuesofI
输出
andC
输出
.
Operatinginthetransientdropoutregioncancause
anincreaseinrecoverytime.thetimerequiredto
recoverfromaloadtransientisafunctionofthe
IMPROVEPSRRANDNOISEPERFORMANCE
magnitudeofthechangeinloadcurrentrate,therate
ofchangeinloadcurrent,andtheavailablehead-
toimproveacperformancesuchaspsrr,输出
房间(v
在
toV
输出
voltagedrop).underworst-情况
噪音,andtransientresponse,itisrecommendedthat
conditions[full-scaleinstantaneousloadchangewith
thePCBbedesignedwithseparategroundplanesfor
(v
在
-v
输出
)closetodcdropoutlevels],thetps731xx
V
在
andV
输出
,witheachgroundplaneconnectedonly
cantakeacoupleofhundredmicrosecondstoreturn
atthegndpinofthedevice.inaddition,theground
tothespecifiedregulationaccuracy.
connectionforthebypasscapacitorshouldconnect
directlytothegndpinofthedevice.
thelowopen-loopoutputimpedanceprovidedbythe
nmospasselementinavoltagefollowerconfigur-
TheTPS731xxinternalcurrentlimithelpsprotectthe
ationallowsoperationwithoutanoutputcapacitorfor
regulatorduringfaultconditions.foldbackcurrent
manyapplications.aswithanyregulator,theaddition
helpstoprotecttheregulatorfromdamageduring
ofacapacitor(nominalvalue1µf)fromtheoutputpin
outputshort-circuitconditionsbyreducingcurrent
togroundwillreduceundershootmagnitudebut
limitwhenV
输出
dropsbelow0.5v.seefigure11in
increaseduration.intheadjustableversion,这
theTypicalCharacteristicssectionforagraphofI
输出
additionofacapacitor,c
FB
,fromtheoutputtothe
vsV
输出
.
adjustpinwillalsoimprovethetransientresponse.
thetps731xxdoesnothaveactivepull-downwhen
theoutputisover-电压.thisallowsapplications
TheEnablepinisactivehighandiscompatiblewith
thatconnecthighervoltagesources,suchasalter-
standardttl-cmoslevels.v
EN
below0.5v(最大值)
natepowersupplies,totheoutput.thisalsoresults
turnstheregulatoroffanddropsthegroundpin
inanoutputovershootofseveralpercentiftheload
currenttoapproximately10na.whenshutdowncapa-
currentquicklydropstozerowhenacapacitoris
bilityisnotrequired,theenablepincanbeconnected
connectedtotheoutput.thedurationofovershoot
toV
在
.whenapull-upresistorisused,andoperation
canbereducedbyaddingaloadresistor.这
downto1.8visrequired,usepull-upresistorvalues
overshootdecaysataratedeterminedbyoutput
below50k
Ω
.
capacitorC
输出
andtheinternal/externalloadresist-
ance.therateofdecayisgivenby:
(fixedvoltageversion)
12
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