ADAU 1701 CM pin, 47 or 10uf?

SigmaDSP & SigmaStudio MCastany Feb 19, 2014 00:00 1 replies Original on forum ↗

MCastany Question

Feb 19, 2014 00:00

Hi,

This question is about the CM pin (40) in the ADAU1701. Reading the datasheet (Page 13), on the CM pin description, they say you have to connect a 47uF decopuling cap:

"1.5 V Common-Mode Reference. Connect a 47 μF decoupling capacitor between this pin and ground to reduce crosstalk between the ADCs and DACs. (...)"

My surprise came when I saw in the evaluation board schematics (adn the board it self) that connected to CM pin there was a 10uF cap (with a decoupling 0.1uF).

Is there any reason for using one cap or another, or it's just an error in the datasheet?

Thank you,

Marti

Audio Signal Processors

eval_adau1701minibz

problem

10uf

47uf

SigmaDSP Audio Processors

evaluation_board

adau1701

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ColemanR Reply

Feb 19, 2014 00:00

Hi Marti,

Thanks for your question, and I apologize for any confusion caused by the discrepancy between the datasheet and eval board.

The decoupling capacitor on the CM pin acts as a filter for audio in the internal reference circuit, and as you can imagine, the quieter the quieter CM reference, the better the performance of the ADAU1701. Crosstalk and low-frequency noise are the specs that are affected the most. We recommend 47 uF in the datasheet because we have found that this value will allow you to reach the best performance that is specified in the datasheet under all conditions. Our EVAL-ADAU1701MINIZ is intended to demonstrate a smaller and less expensive design, that makes some compromises. I would recommend that you design your board with a version of a small 47 uF pcb footprint that would also hold a 22 uF and 10 uF part. Once you have your boards in hand, you can try the various values and see which gives you the performance you require.

Please let me know if you need any more help here.

Regards,

Coleman

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