ADAU1977WBCPZ-R7 datasheet(28/68 Pages) AD

28 / 68 page

ADAU1977

Data Sheet

Rev. C | Page 28 of 68

The bit clock frequency depends on the sample rate, the slot

width, and the number of bit clocks per slot. Table 19 can be

used to calculate the BCLK frequency.

The sample rate (fS) can range from 8 kHz up to 192 kHz.

However, in master mode, the maximum bit clock frequency

(BCLK) is 24.576 MHz. For example, for a sample rate of

192 kHz, 128 × fS is the maximum possible BCLK frequency.

Therefore, only 128 bit clock cycles are available per TDM

frame. There are two options in this case: either operate with a

32-bit data width in TDM4 or operate with a 16-bit data width

in TDM8. In slave mode, this limitation does not exist because

the bit clock and frame clock are fed to the ADAU1977. Various

combinations of BCLK frequency and mode are available, but

care must be taken to choose the combination that is most

suitable for the application.

Connection Options

Figure 30 through Figure 34 show the available options for

connecting the serial audio port in I2S or TDM mode. In TDM

mode, it is recommended to include the pull-down resistor on

the data signal to prevent the line from floating when the

SDATAOUTx pin of ADAU1977 goes high-Z during an inactive

period. The resistor value should be such that no more than

2 mA is drawn from the SDATAOUTx pin. Although the resistor

value is typically in the range of 10 kΩ to 47 kΩ, the appropriate

resistor value depends on the devices on the data bus.

Table 19. Bit Clock Frequency TDM Mode

BCLK Frequency

Mode

16 Bit Clocks Per Slot

24 Bit Clocks Per Slot

32 Bit Clocks Per Slot

TDM2

32 × fS

48 × fS

64 × fS

TDM4

64 × fS

96 × fS

128 × fS

TDM8

128 × fS

192 × fS

256 × fS

TDM16

256 × fS

384 × fS

512 × fS

Figure 30. Serial Port Connection Option 1—I2S/LJ/RJ Mode, ADAU1977 Master

Figure 31. Serial Port Connection Option 2—I2S/LJ/RJ Mode, ADAU1977 Slave

DSP

SLAVE

MASTER

ADAU1977

BCLK

LRCLK

SDATAOUT1

SDATAOUT2

DSP

MASTER

SLAVE

ADAU1977

BCLK

LRCLK

SDATAOUT1

SDATAOUT2

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