STM32MP1 + STPMIC1A PMIC Power issue

[hochul yoo]

Hi ~
I am using STM32MP157C MPU + STPMIC1A for my custom board with ecosystem 4.1
And unfortunately I'm wrestling with some problem regarding PMIC.
I produced 30 boards for sample.
Some board is working fine but some board has power issue.

1) Custom board configuration
My custom board consists of a CPU and BASE board like EV1 Evaluation board.
CPU board has STM32MP157C MPU + STPMIC1A + DDR, eMMC.
Base board has various peripheral such as USB, I/O, HDMI, microSD and so on.

2) PMIC issue
Boot device is eMMC (SDINBDG4-16G-XI1).
STPMIC1A BUCK4's default output level is 3.3V and eMMC use it for VCC.
In some boards without any problem, BUCK4 output 3.3V normally.
In some boards with the problem, BUCK4 output 3.17V abnormally.
Plus, it looks like as following with a cycle time of about 250ms,
As a result, the board fails to boot.
Yellow is 5VIN and Blue is BUCK4 output.

3) VIN Threshold
The first is a picture of a normal board and
the second is a picture of an abnormal board.

4) Others

All the pictures above were tested with the CPU board only, without the base board.
If I connect the BASE board, the BUCK4 voltage level drops to 1.78V.

I attached my schematics.
Please tell me if there are something I should check.

Thank you
Best regards

[PatrickF]

Hi @hochul yoo ,

look like Buck4 is not running properly or overloaded.

Did you use recommended STPMIC1 components (from STPMIC1 datasheet) and recommended layout (from AN5431) ?

Did you excluded manufacturing issues like bad soldering on STPMIC1 and surrounding components ?

Particularly, check correct soldering of STPMIC1 EPGND (which is sometimes hard to get correct soldering due to large area and high thermal conductivity to inner layers)

Did you check for some board shortcircuit which could make Buck4 overcurrent limitation to occur.

Btw, I'm not legal expert, but I think using ST logo in your own schematics drawing is not allowed in case you plan to make them available outside your company.

Regards.

[Vincenzo]

Hi @hochul yoo,

could you check the C99 input cap of Buck4IN and check the PCB layout especially for the connection of the feedback input for Buck4 (Vout_4 pin #27), it must be connected with dedicated track directly on the cross of the inductor and Cout passive components for a good control of the buck converter.

Let me know

Best regards

Vincenzo