Datasheet

V
(rms)
+
V
O(PP)
2 2
Ǹ
Power +
V
(rms)
2
R
L
(8)
R
L
C
C
V
O(PP)
V
O(PP)
V
DD
–3 dB
f
c
R
L
2x V
O(PP)
V
O(PP)
–V
O(PP)
V
DD
V
DD
FULLYDIFFERENTIALAMPLIFIER
f
c
+
1
2pR
L
C
C
(9)
TPA6205A1
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..............................................................................................................................................................SLOS490BJULY2006REVISEDJUNE2008
eliminatestheneedfortheblockingcapacitors.
Low-frequencyperformanceisthenlimitedonlyby
theinputnetworkandspeakerresponse.Costand
PCBspacearealsominimizedbyeliminatingthe
bulkycouplingcapacitor.
Figure33.Single-EndedOutputandFrequency
Figure32.DifferentialOutputConfiguration
Response
Inatypicalwirelesshandsetoperatingat3.6V,
Increasingpowertotheloaddoescarryapenaltyof
bridgingraisesthepowerintoan8-speakerfroma
increasedinternalpowerdissipation.Theincreased
singled-ended(SE,groundreference)limitof200
dissipationisunderstandableconsideringthatthe
mWto800mW.Insoundpowerthatisa6-dB
BTLconfigurationproducestheoutputpowerof
improvement—whichisloudnessthatcanbeheard.
theSEconfiguration.
Inadditiontoincreasedpowertherearefrequency
responseconcerns.Considerthesingle-supplySE
configurationshowninFigure33.Acoupling
EFFICIENCYANDTHERMALINFORMATION
capacitorisrequiredtoblockthedcoffsetvoltage
fromreachingtheload.ThiscapacitorcanbequiteClass-ABamplifiersareinefficient.Theprimarycause
large(approximately33µFto1000µF)soittendstooftheseinefficienciesisvoltagedropacrossthe
beexpensive,heavy,occupyvaluablePCBarea,andoutputstagetransistors.Therearetwocomponents
havetheadditionaldrawbackoflimitingoftheinternalvoltagedrop.Oneistheheadroomor
low-frequencyperformanceofthesystem.Thisdcvoltagedropthatvariesinverselytooutputpower.
frequency-limitingeffectisduetothehighpassfilterThesecondcomponentisduetothesinewavenature
networkcreatedwiththespeakerimpedanceandtheoftheoutput.Thetotalvoltagedropcanbe
couplingcapacitanceandiscalculatedwithcalculatedbysubtractingtheRMSvalueoftheoutput
Equation9.voltagefromV
DD
.Theinternalvoltagedropmultiplied
bytheaveragevalueofthesupplycurrent,I
DD
(avg),
determinestheinternalpowerdissipationofthe
amplifier.
Forexample,a68-µFcapacitorwithan8-speaker
wouldattenuatelowfrequenciesbelow293Hz.The
BTLconfigurationcancelsthedcoffsets,which
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