ADAU1442 TDM4 mode and synchronization with CODECS AD1938

Hi Christian,

I am concerned about clock synchronization in the setup as you have described it. If you are running each AD1938 from its own independent crystal, and driving each codec's LRCLK and BCLK ports from an external device, I think you will have trouble with the AD1938 staying locked - for each codec, there must be synchronicity between MCLK and the port clocks (LRCLK and BCLK). I would recommend that you use LRCLK PLL mode in each of the AD1938 codecs, remove the crystal from each AD1938 and change the loop filter as recommended in the datasheet. You will be able to run the codecs in TDM4 and LRCLK PLL slave mode with no trouble.

Alternately, you could run the AD1938 codecs in Master mode, each with a crystal, and drive your port clocks from the AD1938s to the ADAU1442. I would recommend the first scenario, since it allows you to remove the crystals from your BOM.

Best regards,

Coleman

Thanks Coleman,

it was as well my first planning to set the AD1938 PLL and Clock Control register to LRCLK input (DLRCLK or ALRCLK, regardless of which due to the parallel connection of DLRCKL and ALRCLK pins) for synchronizing with the frame clock of the ADAU1442. It's helpfull to know MCLK is not necessary and TDM4 mode will work.

A little drop of bitterness is the use of the PLL instead of a hardwired clocking, i hope this cause no trouble.

Thanks

Christian