Part Number: PCM2912A
I built a prototype board with the PCM2912A. Works beautifully. One thing I noticed though was the coupling of the 1KHz USB packet frame (and its harmonics) to the Analog Mic signal.
Could this be mitigated simply by putting a ferrite between AGND pin of the chip and my GND plane (I have a single GND plane that all circuitry connects to, and my analog and digital sections are isolated), or is this considered common mode noise on the USB that needs a common mode choke.
This comes up occasionally with these PCM29xx CODECs and the usual root of the situation is that there is 1kHz noise on the supply lines to the PCM2912 that are getting injected one way or another due to the 1kHz USB tone frame.
The solution is to try to minimize the power-supply/GND noise through proper layout, increased power-supply decoupling, and sometimes common-mode chokes to keep the noise out as you've mentioned. You'll probably be able to see the noise on a scope and as you work towards mitigating how it's propagating through your board you'll see it decrease.
Regards,Collin WellsPrecision ADC Applications
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In reply to Collin Wells:
Thanks a lot. One last question pertaining to ESD. I see that the EVM 2912A board doesn't have any ESD chips at the input before the PCM. For production, does TI recommend the use of a USB ESD protection chip before the PCM2912A.
Thanks a lot.
In reply to Taoufiq Bellamine:
Yes, the device does not have any built-in extra IEC level ESD protection inside of it and this should be added externally (TI has options here: https://www.ti.com/interface/circuit-protection/overview.html ) to protect the device.
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