PMIC startup issue

[nlemoult]

Hi,

I am currently using the SiP OSD3358-512M-BSM and am having a problem on the PMIC boot sequence on the last batch of boards made. We have manufactured 2 batches previously without encountering this problem.

On this set of 10 boards, 1 board seems to start nominally and the others do not. I followed a similar topic but adding decoupling to the power input doesn’t seem to have given better results (https://octavosystems.com/forums/topic/osd3358-pmic-startup-problem/).

We had to source the processors from a broker due to component shortages, but we’d like to understand the problem to be sure it’s not a design flaw that we haven’t encountered before.

I measured the signals of the PMIC on the board which starts and on another which presents the problem, here it is in attached image. Could you give me some suggestions to understand if the problem is internal to the SiP or if our design needs improvement? We may privately share our design for investigation.

Regards,
Noel

Attachments:

1. 

   Board1left_Board6right_PMIC_pwrup_seq.png
   

[Neeraj Dantu]

Noel,

Apologies for the late reply. It seems that your post was stuck in our SPAM filter.

Looking at the power up sequencing of the good part vs bad part you attached, it looks like several of the output rails do not come up. Specifically, LDO2, LDO3, DCDC2 and DCDC3 do not come up, indicating a short on 1 or more of these power rails. Can you check for shorts on these power rails?

Shorts like this could be caused if the recommended handling procedures are not followed. If you have more parts, we recommend you bake at 125C for 35 to 48 hours before you try to put them on the boards and reflow. The recommended handling procedure is described in sections 9.2 and 9.3 of the datasheet: https://octavosystems.com/docs/osd335x-sm-datasheet/

If you have X-ray capability, you can image the failed parts to see any solder flow inside the SiP.

Best,

Neeraj

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