How to control external power for a battery powered STM32MP1 product?

iguffick2 · ‎2020-04-28

I'm looking to use the STM32MP1 for a battery powered product.

What is the recommended configuration to control external power supplies?

Both in startup and shutdown.

In the past I've used an external M0 as a power sequencer. Latching the power from a momentary power switch, then signalling a shutdown (via UART or I2C) and powering down once Linux has shutdown.

Is there a way of doing this with just the STM32MP1?

PatrickF · ‎2020-04-29

Hello,

Using VDD (STPMIC1 buck3) to keep your 14V to 5V buck converter ON is probably enough.

VDD is always active, even in STANDBY mode, and is only stopped when the platform is going in OFF mode (e.g. SW request)

Notice that if there is a reset (e.g. NRST activation due to STM32MP15x watchdog), the STPMIC1 will make a complete power cycle (including VDD buck3) which take some tens of ms (see STPMIC1 documentations). So some delay before stopping the 14V to 5V buck is required (which might probably be done using a simple RC).

Regards,

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Olivier GALLIEN · ‎2020-04-28

Hi @iguffick2

ST is providing document AN5260 STM32MP151/153/157 MPU lines and STPMIC1B integration on a battery powered application to help you in design of a battery powered application.

Does it answer your question ?

Olivier

Olivier GALLIEN
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iguffick2 · ‎2020-04-29

Hi Olivier,

That app note is very helpful, I hadn't spotted that one before, so thanks for pointing that out.

It is a very in-depth description for a single cell application.

However, my application would have a 4-cell pack.

So I'd have a circa 14V to 5V regulator before the STPMIC. I could have a power button that enables this regulator, but would need a 'keep alive' from the system so that a controlled power off can be achieved. I could diode steer the power switch to also connect to the PMIC PONKEY input without any problem.

I'd like to figure out a way of using the 16s long press feature to turn off the external regulator. Could I simply monitor one of the generated supplies to keep the enable to the external regulator, then when the 16s long press powers down that supply, the external enable would also be removed?

I'd appreciate if you have any thoughts to share on how I might achieve this.

Regards,

Ian.

PatrickF · ‎2020-04-29

Hello,

Using VDD (STPMIC1 buck3) to keep your 14V to 5V buck converter ON is probably enough.

VDD is always active, even in STANDBY mode, and is only stopped when the platform is going in OFF mode (e.g. SW request)

Notice that if there is a reset (e.g. NRST activation due to STM32MP15x watchdog), the STPMIC1 will make a complete power cycle (including VDD buck3) which take some tens of ms (see STPMIC1 documentations). So some delay before stopping the 14V to 5V buck is required (which might probably be done using a simple RC).

Regards,

In order to give better visibility on the answered topics, please click on 'Accept as Solution' on the reply which solved your issue or answered your question.

iguffick2 · ‎2020-04-29

Hi Patrick,

Very helpful, I should be able to figure out the rest from there.

Thank you both for your help.

Regards,

Ian.