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APPLICATIONINFORMATION
CapacitorRecommendationsforthePTV12010SeriesofPowerModules
InputCapacitors
outputcapacitor(optional)
CeramicCapacitors
TantalumCapacitors
PTV12010L
PTV12010W
SLTS234–DECEMBER2004
therequiredinputcapacitorsareacombinationofa10-µfx5r/x7rceramic,anda100-µfelectrolytictype.
WhenV
O
>3vthe100-µfelectrolyitccapacitancemustberatedfor700marmsripplecurrentcapability.为
V
O
≤
3v,theripplecurrentratingmustbeatleast450marms.whereapplicable,table1givesthemaximum
outputvoltageandcurrentlimitsforacapacitor'srmsripplecurrentrating.theripplecurrentrequirementsforthe
electrolyticcapacitanceare
conditional
thatthe10-µfceramiccapacitorispresent.
the10-µfceramiccapacitorisnecessarytoreduceboththemagnitudeofripplecurrentthroughtheelectroytic
capacitorandtheamountofripplecurrentreflectedbacktotheinputsource.ceramiccapacitorsshouldbe
locatedwithin0.5in.(1,3cm)ofthemoduleinputpins.additionalceramiccapacitorscanbeaddedtoreducethe
rmsripplecurrentrequirementfortheelectrolyticcapacitor.
ripplecurrent(arms)比率,lessthan100m
Ω
ofequivalentseriesresistance(等效串联电阻),andtemperaturearethe
majorconsiderationswhenselectinginputcapacitors.regulartantalumcapacitorshavearecommended
minimumvoltageratingof2
×
(最大值.dcvoltage+acripple).thisisstandardpracticetoensurereliability.onlya
fewtantalumcapacitorswerefoundtohavesufficientvoltageratingtomeetthisrequirement.attemperatures
below0
°
c,theesrofaluminumelectrolyticcapacitorsincreases.fortheseapplicationsos-con,poly-
mer-tantalum,andpolymer-aluminumtypesshouldbeconsidered.
forapplicationswithloadtransients(suddenchangesinloadcurrent),regulatorresponsebenefitsfromexternal
outputcapacitance.theoptionalvaluedefinedisonlyrequiredtomeetthetransientresponsespecification.为
mostapplications,ahigh-qualitycomputer-gradealuminumelectrolyticcapacitorisadequate.thesecapacitors
providedecouplingoverthefrequencyrange,2khzto150khz,andaresuitablewhenambienttemperaturesare
above0
°
c.foroperationbelow0
°
c,tantalum,陶瓷的,oros-contypecapacitorsarerecommended.当
usingoneormorenonceramiccapacitors,thecalculatedequivalentesrshouldbenolowerthan4m
Ω
(7m
Ω
usingthemanufacturer'smaximumesrforasinglecapacitor).alistofpreferredlow-esrtypecapacitorsare
identifiedintable1.
inadditiontoelectrolyticcapacitance,addinga10–µfceramiccapacitoracrosstheoutputwillfurtherreducethe
outputripplevoltageandimprovetheregulator'stransientresponse.themeasurementofboththeoutputripple
andtransientresponseisalsobestachievedacrossa10–µfceramiccapacitor.
above150khz,theperformanceofaluminumelectrolyticcapacitorsislesseffective.multilayerceramic
capacitorshavelowesrandaresonantfrequencyhigherthanthebandwidthoftheregulator.theyare
recommendedtoreducethereflectedripplecurrentattheinputaswellasimprovethetransientresponseofthe
输出.whenusedontheoutputtheircombinedesrisnotcriticalaslongasthetotalvalueofceramic
capacitancedoesnotexceedapproximately300µf.也,topreventtheformationoflocalresonances,donot
placemorethanfiveidenticalceramiccapacitorsinparallelwithvaluesof10µforgreater.
tantalum-typecapacitorscanonlybeusedontheoutputbus,andarerecommendedforapplicationswherethe
ambientoperatingtemperaturecanbelessthan0
°
c.theavxtps,sprague593d/594/595andkemet
t495/t510capacitorseriesaresuggestedovermanyothertantalumtypesduetotheirhigherratedsurge,电源
消耗,andripplecurrentcapability.asacaution,manygeneral-purposetantalumcapacitorshave
considerablyhigheresr,reducedpowerdissipationandlowerripplecurrentcapability.thesecapacitorsare
alsolessreliableastheyhavereducedpowerdissipationandsurgecurrentratings.tantalumcapacitorsthat
havenostatedesrorsurgecurrentratingarenotrecommendedforpowerapplications.
whenspecifyingos-conandpolymertantalumcapacitorsfortheoutput,theminimumesrlimitisencountered
beforethemaximumcapacitancevalueisreached.
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