www.德州仪器.com
decouplingcapacitor(c
S
)
inputcapacitors(c
I
)
f
c
1
2
R
I
C
I
(1)
C
I
1
2
R
I
f
c
(2)
TPA2012D2
SLOS438–DECEMBER2004
thetpa2012d2isahigh-performanceclass-daudioamplifierthatrequiresadequatepowersupplydecoupling
toensuretheefficiencyishighandtotalharmonicdistortion(thd)islow.forhigherfrequencytransients,
尖刺,ordigitalhashontheline,agoodlowequivalent-序列-阻抗(等效串联电阻)ceramiccapacitor,typically1
µf,placedascloseaspossibletothedevicepv
DD
leadworksbest.placingthisdecouplingcapacitorcloseto
thetpa2012d2isimportantfortheefficiencyoftheclass-damplifier,becauseanyresistanceorinductancein
thetracebetweenthedeviceandthecapacitorcancausealossinefficiency.forfilteringlower-frequencynoise
信号,a4.7µforgreatercapacitorplacedneartheaudiopoweramplifierwouldalsohelp,butitisnotrequired
inmostapplicationsbecauseofthehighpsrrofthisdevice.
table1.gainsetting
INPUTIMPEDANCE
GAINGAIN
g1g0(r
I
)
(v/v)(db)
(k
Ω
)
002628.1
0141217.3
108189.8
1116245.2
TheTPA2012D2doesnotrequireinputcouplingcapacitorsifthedesignusesadifferentialsourcethatisbiased
from0.5vtov
DD
-0.8v.iftheinputsignalisnotbiasedwithintherecommendedcommon-modeinputrange,如果
highpassfilteringisneeded(seefigure31),orifusingasingle-endedsource(seefigure32),inputcoupling
capacitorsarerequired.
theinputcapacitorsandinputresistorsformahigh-passfilterwiththecornerfrequency,f
c
,determinedin
equation1.
thevalueoftheinputcapacitorisimportanttoconsiderasitdirectlyaffectsthebass(lowfrequency)
performanceofthecircuit.speakersinwirelessphonescannotusuallyrespondwelltolowfrequencies,sothe
cornerfrequencycanbesettoblocklowfrequenciesinthisapplication.notusinginputcapacitorscanincrease
outputoffset.
equation2isusedtosolvefortheinputcouplingcapacitance.
ifthecornerfrequencyiswithintheaudioband,thecapacitorsshouldhaveatoleranceof
±
10%orbetter,
becauseanymismatchincapacitancecausesanimpedancemismatchatthecornerfrequencyandbelow.
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