PCM2906C

www.ti.com

SBFS037

– NOVEMBER 2011

Clock and Reset

The PCM2906C requires a 12-MHz (

±500 ppm) clock for the USB and audio functions. The clock can be

generated by a built-in oscillator with a 12-MHz crystal resonator. The 12-MHz crystal resonator must be

connected to XTI (pin 21) and XTO (pin 20) with one high-value (1-M

Ω) resistor and two small capacitors, the

capacitance of which depends on the load capacitance of the crystal resonator. An external clock can be

supplied to XTI (pin 21). If an external clock is used, XTO (pin 20) must be left open. Because there is no clock

disabling signal, use of the external clock supply is not recommended. SSPND (pin 28) is unable to use clock

disabling.

The PCM2906C has an internal power-on reset circuit, which triggers automatically when VBUS (pin 3) exceeds

2.5 V typical (2.7 V to 2.2 V). Approximately 700

μs is required until internal reset release.

Digital Audio Interface

The PCM2906 employs S/PDIF for both input and output. Isochronous-out data from the host are encoded to the

S/PDIF output and the DAC analog output. Input data are selected from either the S/PDIF or ADC analog input.

When the device detects S/PDIF input and successfully locks the received data, the isochronous-in transfer data

source automatically selected is S/PDIF; otherwise, the data source selected is the ADC analog input.

This feature is a customer option. It is the responsibility of the user to implement this feature.

Supported Input/Output Data

The following data formats are accepted by S/PDIF for input and output. All other data formats are unusable as

S/PDIF.

•

48-kHz 16-bit stereo

•

44.1-kHz 16-bit stereo

•

32-kHz 16-bit stereo

Any mismatch of the sampling rate between the input S/PDIF signal and the host command is not acceptable.

Any mismatch of the data format between the input S/PDIF signal and the host command may cause unexpected

results, with the following exceptions:

•

Recording in monaural format from stereo data input at the same data rate

•

Recording in 8-bit format from 16-bit data input at the same data rate

A combination of these two conditions is not acceptable.

For playback, all possible data-rate sources are converted to the 16-bit stereo format at the same source data

rate.

Channel Status Information

The channel status information is fixed as consumer application, PCM mode, copyright, and digital/digital

converter. All other bits are fixed as 0's except for the sample frequency, which is set automatically according to

the data received through the USB.

Copyright Management

Isochronous-in data are affected by the serial copy management system (SCMS). When the control bit indicates

that the received digital audio data are original, the input digital audio data are transferred to the host. If the data

are indicated as first generation or higher, the transferred data are routed to the analog input.

Digital audio data output is always encoded as original with SCMS control.

Copyright

© 2011, Texas Instruments Incorporated

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