PCM1795DB datasheet(40/58 Pages) TI

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Application for Interfacing With an External Digital Filter

Pin Assignment When Using the External Digital Filter Interface

Audio Format

MSB

BCK

DATA, DATAL,DATAR

1/4 f

S or1/8fS

WDCK

AudioDataWord=16-Bit

AudioDataWord=32-Bit

AudioDataWord=24-Bit

9 10 11 12 13 14 15

LSB

19 20 21 22 23 24 25 26 27

29 30 31

9 10 11 12 13 14 15

17 18 19

21 22 23

DATA, DATAL,DATAR

MSB

LSB

MSB

LSB

PCM1795

SLES248 – MAY 2009 ........................................................................................................................................................................................................ www.ti.com

For some applications, it may be desirable to use an external digital filter to perform the interpolation function, as

it can provide improved stop-band attenuation when compared to the internal digital filter of the PCM1795.

The PCM1795 supports several external digital filters, including:

• Texas Instruments DF1704 and DF1706

• Pacific Microsonics PMD200 HDCD filter/decoder IC

• Programmable digital signal processors (DSPs)

The external digital filter application mode is accessed by programming the following bits in the corresponding

control register:

• DFTH = 1 (register 20)

The pins used to provide the serial interface for the external digital filter are illustrated in Figure 55. The word

clock (WDCK) signal must be operated at 8 times or 4 times the desired sampling frequency, fS.

• LRCK (pin 4): WDCK as word clock input

• BCK (pin 6): Bit clock for audio data

• DATA (pin 5): Monaural audio data input when the DFMS bit is not set to '1'

• ZEROL (pin 1): DATAL as left channel audio data input when the DFMS bit is set to '1'

• ZEROR (pin 2): DATAR as right channel audio data input when the DFMS bit is set to '1'

The PCM1795 in the external digital filter interface mode supports right-justified audio formats including 16-bit,

24-bit, and 32-bit audio data, as shown in Figure 56. The audio format is selected by the FMT[2:0] bits of control

Figure 56. Audio Data Input Format for External Digital Filter (Internal DF Bypass Mode) Application

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