Will STPMIC1A will be damaged, if we apply 3V3 on LDO2 (default 1V8) for very first boot?

[froesel]

Hi,

we want to use the STPMIC1A for supply of an STM32MP157 custom board and its LDO2 to supply a SD Card. At the moment, a flashing proccess during EOL is not planned and my customer wants to boot from SD Card.

As this LDO2 is programmed as 1V8 by factory, the SD Card will not come up.

We want to increase its voltage by an external power supply during first boot (from SD) and during that, the PMIC will be reprogrammed in a way that LDO2 will supply 3V3, so the external power supply is not needed anymore.

As the LDO2 output voltage is lower than Vin of LDO2 and LDO2 is not monitored,

I did not find any restrictions, which are against my idea.

Can you confirm, that if Vin and LDO25IN is 5V, and LDO2OUT (programmed default as 1V8) is superimposed by 3V3, the PMIC will not be damaged and not shut down?

Thank you,

Florian

[Peter BENSCH]

Why don't you program the NVM of the STPMIC1 so that the LDO2 starts with 3.3V instead of the preset 1.8V? Since the NVM is not volatile, this programming would have to be carried out exactly once:

• either before assembly
• or after assembly by a single programming process

Regards

/Peter

[froesel]

Hi Peter,

totally with you; normally, EOL flashing process is standard. I'm developing an refresh of an existing design and try to change as little as possible in existing production line. As we boot from SD Card, we would like to avoid an additional flashing process of the PMIC during production.

Do you see any restrictions of my idea?

Thanks,

Florian

[Peter BENSCH]

Well, it is rather unusual for LDOs, even discrete ones, to apply a higher output voltage when supplied with an input voltage. The Absolute Max Ratings of the STPMIC1 (datasheet, table 4) mention a permissible voltage range of -0.5V...5V for the LDOxOUT pins, so applying 3.3V seems harmless at first.

Essentially, it comes down to a guess, but you are welcome to open a personal ticket at OLS to get more details or confirmation.

If the problem is solved, please mark this thread as answered by selecting Select as best, as also explained here. This will help other users find that answer faster.

Good luck!

/Peter

[Vincenzo · Accepted solution]

Dear froesel,

from the STPMIC1 DS you can see that LDO2 for A version is programmed with a rank=0, it mean that the regulator is no turned ON @start-up. If the output is in OFF state the internal pull-down is activated and if you will try to apply an external 3.3V an extra consumption is observed with possible damage of the pin (resistor load is designed just for discharging the output capacitor for a short time). My suggestion is to avoid this sequence and jump directly @boot phase to change the NVM content for your needs.

Best Regards

Vincenzo

[froesel]

Hi Vincenzo,

thank you for your advice. I missed, that this regulator is off by default which leads to problems you mentioned.

Thanks,

Florian