Datasheet

CalculationofOutputSignalLevelofTAS5706A/BFeedbackPowerStage
TAS5706A
TAS5706B
SLOS606D–MARCH2009–REVISEDSEPTEMBER2009............................................................................................................................................. www.ti.com
(GainIsindependentofPVCC)
ThegainoftheTAS5706A/Bisthetotaldigitalgainofthecontrollermultipliedbythegainofthepowerstage.
Forahalf-bridgechanneloftheTAS5706A/Bpowerstage,thegainissimply:
Powerstagegain=13×V
RMS
/ModulationLevel
Modulationlevel=fractionoffull-scalemodulationofthePWMsignalattheinputofthepowerstage.
V
RMS
=Audiovoltagelevelattheoutputofthepowerstage=13×ModulationLevel
FortheTAS5706A/Bcontroller,thegainistheprogrammeddigitalgainmultipliedbyascalingfactor,calledthe
maximummodulationlevel.Themaximummodulationlevelisderivedfromthemodulationlimitprogrammedin
thecontroller,whichlimitsdutycycletoasetnumberofpercentabove0%andbelow100%.Settingthe
modulationlimitto97.7%(default)limitsthedutycyclebetween2.3%and97.7%.
Controllergain=digitalgain×maximummodulationlevel×(modulationlevel/digitalFFS)
DigitalFFS=digitalinputfractionoffullscale
Modulationlimit=97.7%
Maximummodulationlevel=2×modulationlimit–1=0.954
TheoutputsignalleveloftheTAS5706A/Bcannowbecalculated.
V
RMS
=digitalFFS×digitalgain×maximummodulationlevel×13
Withthemodulationlimitsetatthedefaultlevelof97.7%,thisbecomes:
V
RMS
=digitalFFS×digitalgain×12.4(Single-ended)
V
RMS
=digitalFFS×digitalgain×24.8(BTL)
Example:Input=–20dbFS;volume=0dB;biquads=ALLPASS;modulationindex=97.7%;mode=BTL
OutputV
RMS
=24.8×0.1×1=2.48V
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TAS5706A is Not Recommended for New Designs