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ADAU1372 TDM8 + 32K Problem.

Question asked by 曾炳阳 on Oct 24, 2016
Latest reply on Nov 1, 2016 by DaveThib

I am using two ADAU1372 chip to get 8 channel ADC & 2 channel DAC using TDM8 Mode.

 

Now we got our first PCB board and start to work.

 

After set the registers , we found the TDM8 mode has some problem at sample rate of 32KHz .

 

our setting:

MCLK = 12.288 XTAL.

PLL = OFF.

 

Reg: 0x32SAI_0)= 0x75left justifiedTDM832KHz fs

Reg: 0x33SAI_1)= 0x65

 

TDM8 Mode , 16 bclk cycle per channel, Master mode.

We directly connect the output data pin to the input data pin to loop back the mic to the dac.

 

Result:

1:We got bclk = 6.144MHz. and LRCLK=32KHz.

2: we can hear the loop back audio , but it is the wrong one which different from what we just said.

3: we check the signal: one LRCLK have 192bit BCLK, there is no data while bclk (128bit-192bit).

 

I think the bclk should be 4.096MHz, Because 32K * 8 * 16(cycles per channel) = 4.096MHz.

And one LRCLK should have 128bit BCLK.

I don't know why bclk = 6.144MHz happen while 32KHz. 

 

Another test:

 

48K Hz , TDM8,-->  Bclk = 6M.  loop back audio test passed.

48K Hz,  TDM4, --> Bclk = 3M.   loop back audio test passed.

32K Hz,  TDM8,--> Bclk = 6M.   loop back audio test failed.

 

I2S + 32K ,BCLK = 1M  --> Fine.

I2s + 16k ,bclk = 512k --> Fine

 

I want to get a bclk = 4.096MHz at 32KHz TDM8 Mode.

Anyone can help me out?

 

   Thanks.

 

Attached files:

1: signal picture TDM8+32K.

2: sch file.

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