PCM1748ESLASH2K datasheet(9/20 Pages) BURR-BROWN

9 / 20 page

PCM1748

SBAS165

FIGURE 3. Audio Data Input Formats.

AUDIO SERIAL INTERFACE

The audio serial interface for the PCM1748 is comprised of

a 3-wire synchronous serial port. It includes LRCK (pin 3),

BCK (pin 1), and DATA (pin 2). BCK is the serial audio bit

clock, and is used to clock the serial data present on DATA

into the audio interface’s serial shift register. Serial data is

clocked into the PCM1748 on the rising edge of BCK.

LRCK is the serial audio left/right word clock used to latch

serial data into the serial audio interface’s internal registers.

Both LRCK and BCK should be synchronous to the

system clock. Ideally, it is recommended that LRCK and

BCK be derived from the system clock input, SCK. LRCK

is operated at the sampling frequency, fS. BCK may be

operated at 32, 48, or 64 times the sampling frequency.

Internal operation of the PCM1748 is synchronized with

LRCK. Accordingly, it is held when the sampling rate

clock of LRCK is changed or SCK and/or BCK is broken at

least for one clock cycle. If SCK, BCK, and LRCK are

provided continuously after this hold condition, the internal

operation will be resynchronized automatically, less than 3/fS

period. In this resynchronize period, and following 3/fS,

analog output is forced to the bipolar zero level, or VCC/2.

External resetting is not required.

AUDIO DATA FORMATS AND TIMING

The PCM1748 supports industry-standard audio data formats,

including Standard, I2S, and Left-Justified, as shown in

Figure 3. Data formats are selected using the format bits,

FMT[2:0], in Control Register 20. The default data format is

24-bit left justified. All formats require Binary Two’s Comple-

ment, MSB-first audio data. See Figure 4 for a detailed timing

diagram of the serial audio interface.

1/f

L-Channel

R-Channel

LRCK

BCK

(= 48 or 64f

18-Bit Right-Justified

DATA

(2) I

2S Data Format: L-Channel = LOW, R-Channel = HIGH

(3) Left-Justified Data Format: L-Channel = HIGH, R-Channel = LOW

(1) Standard Data Format: L-Channel = HIGH, R-Channel = LOW

1/f

L-Channel

R-Channel

LRCK

BCK

(= 32, 48 or 64f

N-2 N-1 N

1/f

L-Channel

R-Channel

LRCK

BCK

(= 32, 48 or 64f

N-2 N-1 N

14 15 16

16 17 18

18 19 20

14 15 16

DATA

22 23 24

DATA

18 19 20

DATA

16 17 18

DATA

24-Bit Right-Justified

14 15 16

22 23 24

18 19 20

17 18

20-Bit Right-Justified

LSB

MSB

LSB

MSB

LSB

MSB

LSB

MSB

LSB

MSB

LSB

MSB

LSB

MSB

LSB

MSB

LSB

MSB

LSB

MSB

LSB

MSB

LSB

MSB

14 15 16

DATA

16-Bit Right-Justified, BCK = 32f

14 15 16

LSB

MSB

LSB

MSB

16-Bit Right-Justified, BCK = 48f

S or 64fS

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