www.德州仪器.com
TransientResponse
下面-voltagelock-输出(uvlo)
MinimumLoad
ThermalInformation
ThermalProtection
PowerDissipation
P
D
V
在
V
输出
I
输出
(2)
PackageMounting
tps79901,tps79915,tps79916,tps79918
tps79925,tps79927,tps79928,tps799285
tps79929,tps79930,tps79932,tps79933
SBVS056C–JANUARY2005–REVISEDMAY2005
aswithanyregulator,increasingthesizeoftheoutputcapacitorwillreduceover/undershootmagnitudebut
increasedurationofthetransientresponse.intheadjustableversion,addingc
FB
betweenOUTandFBwill
improvestabilityandtransientresponse.thetransientresponseofthetps799xxisenhancedbyanactive
拉-downthatengageswhentheoutputovershootsbyapproximately5%ormorewhenthedeviceisenabled.
whenenabled,thepull-downdevicebehaveslikea350
Ω
resistortoground.
thetps799xxutilizesanunder-voltagelock-outcircuittokeeptheoutputshutoffuntilinternalcircuitryis
operatingproperly.theuvlocircuithasade-glitchfeaturesothatitwilltypicallyignoreundershoottransients
ontheinputiftheyarelessthan50µsduration.
thetps799xxisstableandwell-behavedwithnooutputload.tomeetthespecifiedaccuracy,aminimumload
of500µaisrequired.below500µaatjunctiontemperaturesnear+125°c,theoutputcandriftupenoughto
causetheoutputpull-downtoturnon.theoutputpull-downwilllimitvoltagedriftto5%typicallybutground
currentcouldincreasebyapproximately50µa.intypicalapplications,thejunctioncannotreachhigh
temperaturesatlightloadssincethereisnoappreciabledissipatedpower.thespecifiedgroundcurrentwould
thenbevalidatnoloadinmostapplications.
thermalprotectiondisablestheoutputwhenthejunctiontemperaturerisestoapproximately+165°c,准许
thedevicetocool.whenthejunctiontemperaturecoolstoapproximately+145°ctheoutputcircuitryisagain
使能.dependingonpowerdissipation,thermalresistance,andambienttemperature,thethermalprotection
circuitmaycycleonandoff.thiscyclinglimitsthedissipationoftheregulator,protectingitfromdamagedueto
overheating.
Anytendencytoactivatethethermalprotectioncircuitindicatesexcessivepowerdissipationoraninadequate
散热器.forreliableoperation,junctiontemperatureshouldbelimitedto+125°cmaximum.toestimatethe
marginofsafetyinacompletedesign(includingheatsink),increasetheambienttemperatureuntilthethermal
protectionistriggered;useworst-caseloadsandsignalconditions.forgoodreliability,thermalprotectionshould
triggeratleast+35°cabovethemaximumexpectedambientconditionofyourparticularapplication.这个
configurationproducesaworst-casejunctiontemperatureof+125°catthehighestexpectedambient
temperatureandworst-caseload.
theinternalprotectioncircuitryofthetps799xxhasbeendesignedtoprotectagainstoverloadconditions.它
wasnotintendedtoreplaceproperheatsinking.continuouslyrunningthetps799xxintothermalshutdownwill
degradedevicereliability.
theabilitytoremoveheatfromthedieisdifferentforeachpackagetype,presentingdifferentconsiderationsin
thepcblayout.thepcbareaaroundthedevicethatisfreeofothercomponentsmovestheheadfromthe
devicetotheambientair.performancedataforjedeclow-andhigh-kboardsaregiveninthe
消耗
比率
表格.usingheaviercopperwillincreasetheeffectivenessinremovingheatfromthedevice.这
additionofplatedthrough-holestoheat-dissipatinglayerswillalsoimprovetheheatsinkeffectiveness.
powerdissipationdependsoninputvoltageandloadconditions.powerdissipationisequaltotheproductofthe
outputcurrenttimethevoltagedropacrosstheoutputpasselement,asshowninEquation2:
solderpadfootprintrecommendationsforthetps799xxareavailablefromthetexasinstruments'websiteat
www.德州仪器.com.
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