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容积,sediff,andsemaxoperation
TPA6011A4
SLOS392A–FEBRUARY2002–REVISEDJULY2004
figure31.shutdownsequenceinthefigure32.shutdownsequenceinthe
fade-onmodefade-offmode
threepinslabeledvolume,sediff,andsemaxcontrolthebtlvolumewhendrivingspeakersandthese
volumewhendrivingheadphones.allofthesepinsarecontrolledwithadcvoltage,whichshouldnotexceed
V
DD
.
whendrivingspeakersinbtlmode,thevolumepinistheonlypinthatcontrolsthegain.table1showsthe
gainforthebtlmode.thevoltageslistedinthetableareforv
DD
=5v.foradifferentv
DD
,thevaluesinthe
tablescalelinearly.ifv
DD
=4v,multiplyallthevoltagesinthetableby4v/5v,or0.8.
thetpa6011a4allowstheusertospecifyadifferencebetweenbtlgainandsegain.thisisdesirabletoavoid
anylisteningdiscomfortwhenplugginginheadphones.whenswitchingtosemode,thesediffandsemax
pinscontrolthesinge-endedgainproportionaltothegainsetbythevoltageonthevolumepin.whensediff
=0v,thedifferencebetweenthebtlgainandthesegainis6db.refertothesectionlabeled
bridged-系
loadversussingle-endedload
foranexplanationonwhythegaininbtlmodeis2xthatofsingle-endedmode,
or6dbgreater.asthevoltageonthesediffterminalisincreased,thegaininsemodedecreases.thevoltage
ontheSEDIFFterminalissubtractedfromthevoltageontheVOLUMEterminalandthisvalueisusedto
determinethesegain.
someaudiosystemsrequirethatthegainbelimitedinthesingle-endedmodetoalevelthatiscomfortablefor
headphonelistening.mostvolumecontroldevicesonlyhaveoneterminalforsettingthegain.forexample,ifthe
speakergainis20db,thegainintheheadphonechannelisfixedat14db.thislevelofgaincouldcause
discomforttolistenersandtheSEMAXpinallowsthedesignertolimitthisdiscomfortwhenpluggingin
headphones.thesemaxterminalcontrolsthemaximumgainforsingle-endedmode.
thefunctionalityofthesediffandsemaxpinarecombinedtosetthesegain.ablockdiagramofthe
combinedfunctionalityisshowninfigure33.thevalueobtainedfromtheblockdiagramforse_volumeisa
dcvoltagethatcanbeusedinconjunctionwithtable2todeterminethesegain.又一次,thevoltageslistedin
thetableareforV
DD
=5v.thevaluesmustbescaledforothervaluesofv
DD
.
table1andtable2showarangeofvoltagesforeachgainstep.thereisagapinthevoltagebetweeneach
gainstep.thisgaprepresentsthehysteresisabouteachtrippointintheinternalcomparator.thehysteresis
ensuresthatthegaincontrolismonotonicanddoesnotoscillatefromonegainsteptoanother.ifa
potentiometerisusedtoadjustthevoltageonthecontrolterminals,thegainincreasesasthepotentiometeris
turnedinonedirectionanddecreasesasitisturnedbacktheotherdirection.thetrippoint,wherethegain
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