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DROPOUTVOLTAGE
BOARDLAYOUTRECOMMENDATIONTO
TRANSIENTRESPONSE
INTERNALCURRENTLIMIT
关闭
dV
dt
V
输出
C
输出
80k
(4)
tps73201,tps73215,tps73216
tps73218,tps73225,tps73230
tps73233,tps73250
SBVS037F–AUGUST2003–REVISEDSEPTEMBER2004
Thisnoisereductioneffectisshownas
RMSNoise
VoltagevsC
NR
inthetypicalcharacteristicssection.
TheTPS732xxusesanNMOSpasstransistorto
thetps73201adjustableversiondoesnothavetheachieveextremelylowdropout.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.
thetps732xxusesaninternalchargepumptoforlargestepchangesinloadcurrent,thetps732xx
developaninternalsupplyvoltagesufficienttodriverequiresalargervoltagedropfromV
在
toV
输出
至
thegateoftheNMOSpasselementaboveV
输出
.theavoiddegradedtransientresponse.theboundaryof
chargepumpgenerates~250µVofswitchingnoiseatthistransientdropoutregionisapproximatelytwice
~2mhz;不管怎样,承担-pumpnoisecontributionisthedcdropout.valuesofv
在
-v
输出
abovethisline
negligibleattheoutputoftheregulatorformostinsurenormaltransientresponse.
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],thetps732xx
V
在
andV
输出
,witheachgroundplaneconnectedonly
cantakeacoupleofhundredmicrosecondstoreturn
atthegndpinofthedevice.inaddition,theground
tothespecifiedregulationaccuracy.
connectionforthebypasscapacitorshouldconnect
directlytothegndpinofthedevice.
thelowopen-loopoutputimpedanceprovidedbythe
nmospasselementinavoltagefollowerconfigur-
TheTPS732xxinternalcurrentlimithelpsprotectthe
ationallowsoperationwithoutanoutputcapacitorfor
regulatorduringfaultconditions.foldbackhelpsto
manyapplications.aswithanyregulator,theaddition
protecttheregulatorfromdamageduringoutput
ofacapacitor(nominalvalue1µf)fromtheoutputpin
短的-circuitconditionsbyreducingcurrentlimitwhen
togroundwillreduceundershootmagnitudebut
V
输出
dropsbelow0.5v.seefigure11inthetypical
increaseduration.intheadjustableversion,这
CharacteristicssectionforagraphofI
输出
vsV
输出
.
additionofacapacitor,c
FB
,fromtheoutputtothe
adjustpinwillalsoimprovethetransientresponse.
thetps732xxdoesnothaveactivepull-downwhen
TheEnablepinisactivehighandiscompatiblewith
theoutputisover-电压.thisallowsapplications
standardttl-cmoslevels.v
EN
below0.5v(最大值)
thatconnecthighervoltagesources,suchasalter-
turnstheregulatoroffanddropsthegroundpin
natepowersupplies,totheoutput.thisalsoresults
currenttoapproximately10na.whenshutdowncapa-
inanoutputovershootofseveralpercentiftheload
bilityisnotrequired,theenablepincanbeconnected
currentquicklydropstozerowhenacapacitoris
toV
在
.whenapull-upresistorisused,andoperation
connectedtotheoutput.thedurationofovershoot
downto1.8visrequired,usepull-upresistorvalues
canbereducedbyaddingaloadresistor.这
below50k
Ω
.
overshootdecaysataratedeterminedbyoutput
capacitorC
输出
andtheinternal/externalloadresist-
ance.therateofdecayisgivenby:
(fixedvoltageversion)
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