[i.mx8m nano] PMIC damage. Question on "VDD_SOC to GND resistance"

[yan_ding]

Hi,

We are working on PCBA bring up. Two of the prototypes were damaged after a few power cycles. They have the same problem -- PMIC damage (PCA9450BHNY). 

1. I measured the "resistances to GND" for each power rail, and noticed the VDD_SOC to GND was only 2ohm (damaged board).

2. For good boards, the VDD_SOC to GND were 50ohm ~ 70ohm. However, values for other power rails were around 1Kohm.

3. VDD_SOC to GND resistance on bare board was normal.

If the 50~70 ohm value is not correct, what could be the possible reason?

We are using "nano" processor, but still connected the K12, K13, L11, L13, M13, M14, N11 to VDD_SOC (like reference design).

Design guide recommended to tie MIPI-CSI to GND if unused. Should I connect them direct to GND or through a resistor?

Thanks.

[guoweisun]

How many boards do you have?each one has PMIC damage?

[yan_ding]

We made 5 sample boards. 2 of them have PMIC damaged. However, VDD_SOC to GND resistance values are in the same range for good boards. I removed the damaged PMIC, measured again and still get similar value.

[guoweisun]

If you have three boards works well, I think should be assembly or solder issue for the two issue boards.

Could you check them firstly?

[yan_ding]

The good boards also have 50ohm ~ 70ohm resistance between VDD_SOC and GND. Is this typical for imx8m nano? (After removing PMIC the value was still 50ohm ~ 70ohm)

[guoweisun]

I test the resistance between VDD_SOC and ground in I.MX8M nano EVB,the value is about 70OHM.

Attached is the schematic here.

[yan_ding]

That's a very helpful information. The value is typical, although it is a little strange to me. Let me examine the boards for other possible reason. Thanks a lot.

[guoweisun]

what's the result if you do cross test? for example change the good PMIC into bad board.

Do you mind to share with your PMIC related circuit?

[yan_ding]

Hi,

Thanks you for response. We replaced the damaged PMIC with a good one. The new PMIC damaged again after a few power cycle. May I share the design file in private?

[ksc123]

Hello Yan,
Have got any resolution on this VDD_SOC short to GND.
I am facing the same issue with i.MX8M Plus processor.