STPMIC1 Always ON LDO for powering a supporting micro (3.3V)?

[roland van straten]

I have a small micro that needs to run before the MP157 is active. The voltage coming gin is 5V, but I need 3.3V. Is there an always-on LDO in the STPMIC1 for such purpose? I assume the internal LDO is not te be used?

Do I need to program the voltage of the LDO or is it set by default to 3.3V

Regards

[Vincenzo]

Hi,

version of STPMIC1? A, B or...?

To have the 3.3V @Rank1 you need to program (one time, output voltage and Rank#) the LDO# in the NVM content so it will start at turn ON phase.

The STPMIC1 I²C programming guide - Application note

Regards

Vincenzo

[PatrickF · Accepted solution]

Hi @roland van straten 

on STPMIC1A, you could use Buck3 which is started at 3.3V few tens of ms before the MP157 is out of reset and maintained on every modes including Standby. If you need more time, you could maintain the NRST low form your small MCU the time you need.

During operation of STM32MP15x, Buck3 is usually defined as 'no power cycle on NRST' within TF-A in our SW deliveries (e.g. Buck3 kept powered even when watchdog reset occurs after TF-A starts).

Obviously, a platform shutdown requesting an STPMIC1 power-off will make the Buck3 OFF as well.

Regards.

[roland van straten]

Thanks for the note:

I measured the -DK2 and the behavior of BUCK3, LDO2 etc and indeed the STPMIC1A is 3.3V and stable and always on. The LDO e.a. are affected when reset occurs.

Tnx

[Vincenzo]

Hi roland van straten,

you need to program the below address, see STPMIC1 DS rev.10 @page83

set bit to 1 active mask reset option for selected LDO for next

reset power-cycle. It is a single shot option and then register is reset to default

Regards

Vincenzo