Datasheet

ClockandReset
DigitalAudioInterface
SupportedInput/OutputData
ChannelStatusInformation
CopyrightManagement
PCM2906B
www.ti.com ...........................................................................................................................................................................................SLES227–DECEMBER2008
ThePCM2906Brequiresa12-MHz(±500ppm)clockfortheUSBandaudiofunctions.Theclockcanbe
generatedbyabuilt-inoscillatorwitha12-MHzcrystalresonator.The12-MHzcrystalresonatormustbe
connectedtoXTI(pin21)andXTO(pin20)withonehigh-value(1-MΩ)resistorandtwosmallcapacitors,the
capacitanceofwhichdependsontheloadcapacitanceofthecrystalresonator.Anexternalclockcanbe
suppliedtoXTI(pin21).Ifanexternalclockisused,XTO(pin20)mustbeleftopen.Becausethereisnoclock
disablingsignal,useoftheexternalclocksupplyisnotrecommended.SSPND(pin28)isunabletouseclock
disabling.
ThePCM2906Bhasaninternalpower-onresetcircuit,whichtriggersautomaticallywhenV
BUS
(pin3)exceeds
2.5Vtypical(2.7Vto2.2V).Approximately700µsisrequireduntilinternalresetrelease.
ThePCM2906employsS/PDIFforbothinputandoutput.Isochronous-outdatafromthehostareencodedtothe
S/PDIFoutputandtheDACanalogoutput.InputdataareselectedfromeithertheS/PDIForADCanaloginput.
WhenthedevicedetectsS/PDIFinputandsuccessfullylocksthereceiveddata,theisochronous-intransferdata
sourceautomaticallyselectedisS/PDIF;otherwise,thedatasourceselectedistheADCanaloginput.
Thisfeatureisacustomeroption.Itistheresponsibilityoftheusertoimplementthisfeature.
ThefollowingdataformatsareacceptedbyS/PDIFforinputandoutput.Allotherdataformatsareunusableas
S/PDIF.
•48-kHz16-bitstereo
•44.1-kHz16-bitstereo
•32-kHz16-bitstereo
AnymismatchofthesamplingratebetweentheinputS/PDIFsignalandthehostcommandisnotacceptable.
AnymismatchofthedataformatbetweentheinputS/PDIFsignalandthehostcommandmaycauseunexpected
results,withthefollowingexceptions:
•Recordinginmonauralformatfromstereodatainputatthesamedatarate
•Recordingin8-bitformatfrom16-bitdatainputatthesamedatarate
Acombinationofthesetwoconditionsisnotacceptable.
Forplayback,allpossibledata-ratesourcesareconvertedtothe16-bitstereoformatatthesamesourcedata
rate.
Thechannelstatusinformationisfixedasconsumerapplication,PCMmode,copyright,anddigital/digital
converter.Allotherbitsarefixedas0'sexceptforthesamplefrequency,whichissetautomaticallyaccordingto
thedatareceivedthroughtheUSB.
Isochronous-indataareaffectedbytheserialcopymanagementsystem(SCMS).Whenthecontrolbitindicates
thatthereceiveddigitalaudiodataareoriginal,theinputdigitalaudiodataaretransferredtothehost.Ifthedata
areindicatedasfirstgenerationorhigher,thetransferreddataareroutedtotheanaloginput.
DigitalaudiodataoutputisalwaysencodedasoriginalwithSCMScontrol.
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Not Recommended for New Designs