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APPLICATIONINFORMATION
电源-supplyconsiderations
在
OC1
EN1
OC2
2
8
5
7
0.1
µ
F 22
µ
F
0.1
µ
F 22
µ
F
加载
加载
OUT1
OUT2
电源 供应
2.7 v 至 5.5 v
6
EN2
3
4
地
0.1
µ
F
TPS2042B
1
OVERCURRENT
OCRESPONSE
tps2041b,,tps2042b
tps2043b,tps2044b,tps2051b
tps2052b,tps2053b,tps2054b
SLVS514E–APRIL2004–REVISEDJANUARY2006
figure28.typicalapplication(例子,tps2042b)
a0.01-µfto0.1-µfceramicbypasscapacitorbetweeninandgnd,closetothedevice,isrecommended.
placingahigh-valueelectrolyticcapacitorontheoutputpin(s)isrecommendedwhentheoutputloadisheavy.
thisprecautionreducespower-supplytransientsthatmaycauseringingontheinput.additionally,bypassingthe
outputwitha0.01-µfto0.1-µfceramiccapacitorimprovestheimmunityofthedevicetoshort-circuittransients.
asensefetisemployedtocheckforovercurrentconditions.unlikecurrent-senseresistors,sensefetsdonot
increasetheseriesresistanceofthecurrentpath.whenanovercurrentconditionisdetected,thedevice
maintainsaconstantoutputcurrentandreducestheoutputvoltageaccordingly.completeshutdownoccursonly
ifthefaultispresentlongenoughtoactivatethermallimiting.
threepossibleoverloadconditionscanoccur.inthefirstcondition,theoutputhasbeenshortedbeforethe
deviceisenabledorbeforeV
i(在)
hasbeenapplied(看Figure14通过Figure17).thetps204xb/tps205xb
sensestheshortandimmediatelyswitchesintoaconstant-currentoutput.
inthesecondcondition,ashortoranoverloadoccurswhilethedeviceisenabled.attheinstanttheoverload
occurs,highcurrentsmayflowforashortperiodoftimebeforethecurrent-limitcircuitcanreact.afterthe
电流-limitcircuithastripped(reachedtheovercurrenttripthreshold),thedeviceswitchesintoconstant-电流
模式.
inthethirdcondition,theloadhasbeengraduallyincreasedbeyondtherecommendedoperatingcurrent.这
currentispermittedtoriseuntilthecurrent-limitthresholdisreachedoruntilthethermallimitofthedeviceis
超过(看Figure18通过Figure21).thetps204xb/tps205xbiscapableofdeliveringcurrentuptothe
电流-limitthresholdwithoutdamagingthedevice.oncethethresholdhasbeenreached,thedeviceswitches
intoitsconstant-currentmode.
theocxopen-drainoutputisasserted(activelow)whenanovercurrentorovertemperatureshutdowncondition
isencounteredaftera10-msdeglitchtimeout.theoutputremainsasserteduntiltheovercurrentor
overtemperatureconditionisremoved.connectingaheavycapacitiveloadtoanenableddevicecancausea
momentaryovercurrentcondition;不管怎样,nofalsereportingonocxoccursduetothe10-msdeglitchcircuit.
thetps204xb/tps205xbisdesignedtoeliminatefalseovercurrentreporting.theinternalovercurrentdeglitch
eliminatestheneedforexternalcomponentstoremoveunwantedpulses.ocxisnotdeglitchedwhentheswitch
isturnedoffduetoanovertemperatureshutdown.
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