STM32MP1 - VBAT characteristics - need clarity

[ARama.1]

Hi,

we're using STM32MP1 for our project. we have connected super cap to VBAT.

our expectation is to have VBAT supply power to RTC *alone*. we dont want RAM content to be retained. so that RTC shall remain powered for long time. currently the VBAT is supplying back up power for both RAM contents & also for RTC, so we're experiencing RTC back up for just 5 hours instead of expected 5 days. Kindly help out.

 

should we use RREN/BREN in this case?

[PatrickF]

Hi @ARama.1 

To explain the result far below your expectations, I think BREN and RREN are set, so you should change SW (TF-A or opTEE) or DT to remove this setting.

According to datasheet, power with LSE+RTC only should be typically 1.25uA at 3V

Regards.