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CLASS-DOPERATION
TraditionalClass-DModulationScheme
0 V
−12 V
+12 V
Current
OUTP
Differential Voltage
Across Load
OUTN
TPA3008D2ModulationScheme
TPA3008D2
SLOS435A–MAY2004–REVISEDJULY2004
APPLICATIONINFORMATION(continued)
Thissectionfocusesontheclass-DoperationoftheTPA3008D2.
Thetraditionalclass-Dmodulationscheme,whichisusedintheTPA032D0xfamily,hasadifferentialoutput
whereeachoutputis180degreesoutofphaseandchangesfromgroundtothesupplyvoltage,V
CC
.Therefore,
thedifferentialprefilteredoutputvariesbetweenpositiveandnegativeV
CC
,wherefiltered50%dutycycleyields
0Vacrosstheload.Thetraditionalclass-Dmodulationschemewithvoltageandcurrentwaveformsisshownin
Figure17.Notethatevenatanaverageof0Vacrosstheload(50%dutycycle),thecurrenttotheloadishigh,
causinghighlossandthuscausingahighsupplycurrent.
Figure17.TraditionalClass-DModulationScheme'sOutputVoltageandCurrentWaveformsIntoan
InductiveLoadWithNoInput
TheTPA3008D2usesamodulationschemethatstillhaseachoutputswitchingfrom0tothesupplyvoltage.
However,OUTPandOUTNarenowinphasewitheachotherwithnoinput.ThedutycycleofOUTPisgreater
than50%andOUTNislessthan50%forpositiveoutputvoltages.ThedutycycleofOUTPislessthan50%and
OUTNisgreaterthan50%fornegativeoutputvoltages.Thevoltageacrosstheloadsitsat0Vthroughoutmost
oftheswitchingperiod,greatlyreducingtheswitchingcurrent,whichreducesanyI
2
Rlossesintheload.
13