PCM6240-Q1: MICBIAS Output Abnormal

Hi Xiaowei,

Many in our team are out of office right now, please allow until next week to receive a response.

Best,

Garret

Hi team，

Can you please help on this case? Thanks

Best Regards,

Xiaowei Zhang

Hi team,

Today we have replicate this issue again. When issue happens, we test the pin voltage and found the U33S_PERI=BSTVDD=2.1V, BSTOUT=1.6V, and MICBIAS=1.2V. In normal condition U33S_PERI should be 3.3V, so we doubt that PCM6260 cause the U33S_PERI 3.3V drop.

Then we disconnect the L1401 in this issue condition without power off the board, U33S_PERI recover to 3.3V.  And after we power off the board and reconnect the L1401, then power on, the issue disappear.

Have you met such issue before? And can you please provide some suggestions for issue analysis?

Best Regards,

Xiaowei Zhang

Hi,

I suggest removing the schottky diodes on the pull up of each input line to MICBIAS. 

I also suggest placing the unit with MICBIAS error on an EVM and placing a new IC on the customer test board without the diodes.

Hi Daveon,

Daveon Douglas said:

I suggest removing the schottky diodes on the pull up of each input line to MICBIAS. 

I will ask customer to try this.

Daveon Douglas said:

I suggest removing the schottky diodes on the pull up of each input line to MICBIAS. 

This circuit has MP for million units on different projects before, but never met this issue.

Xiaowei Zhang said:

Then we disconnect the L1401 in this issue condition without power off the board, U33S_PERI recover to 3.3V.  And after we power off the board and reconnect the L1401, then power on, the issue disappear.

So is it possible that PCM6260 cause the U33S_PERI drop? This issue is very very different to replicate, what we should to test when met this issue next time?

Best Regards,

Xiaowei Zhang

Hi Xiaowei,

I missed your comment about the inductor. We typically recommend a 600Ohm at 100MHz inductor here. It is possible for the current inductor to be too large, which slows the charge of BSTVDD, delay startup, or limit current and lead to MICBIAS undervoltage.

The exact inductor used on our EVM is listed in the user's guide.

Hi Daveon,

Daveon Douglas said:

It is possible for the current inductor to be too large, which slows the charge of BSTVDD, delay startup, or limit current and lead to MICBIAS undervoltage.

It is not a 100% duplicate issue, most of time the board works well. It will take 2-3 days even more time to replicate this issue.

Best Regards,

Xiaowei Zhang

Hi Daveon,

Daveon Douglas said:

We typically recommend a 600Ohm at 100MHz inductor here. It is possible for the current inductor to be too large, which slows the charge of BSTVDD, delay startup, or limit current and lead to MICBIAS undervoltage.

I didn't see 600Ohm at 100MHz inductor is used when I review the EVM user guide.

The results we observe is the BSTVDD always 2.1V when issue occurs. So is it possible that PCM6260 cause the U33S_PERI drop? U33S_PERI is 3.3V when the board works well.

Best Regards,

Xiaowei Zhang

HI Xiaowei,

Yes, i think that could be the issue. BSTVDD supply should be a stable 3.3V.

As a sanity check for proper operation, BSTOUT should always be ~1V-1.5V higher than the programmed MICBIAS value.

Hi Daveon,

Daveon Douglas said:

Yes, i think that could be the issue. BSTVDD supply should be a stable 3.3V.

Does PCM6260 have register to indicate BSTVDD error or Boost in abnormal operation? We don't see any register abnormal when this issue happens.

Best Regards,

Xiaowei Zhang