Does STM32MP15x support VBAT battery charging?

[Dat Tran]

I could not find any information relates to vbat battery charging in user manual or datasheet.

Is this feature supported in STM32MP15x?

Thanks,

[waclawek.jan]

JW

[Dat Tran]

Yes, thank you so much. Not sure why I didn't see it before.

[Dat Tran]

By the way, do we have any built-in driver that enable charging?

example we have rtcwake to set alarm

do we have something line rtccharge .... to enable charging?

Thanks

[OlivierK · Accepted solution]

Hi Dat Tran (Community Member)

In OSTL (DV4.1) The optee driver enables it.

arch/arm/plat-stm32mp1/drivers/stm32mp1_pwr.c

..

    if (fdt_getprop(fdt, node, "st,enable-vbat-charge", NULL)) {

        uintptr_t cr3 = stm32_pwr_base() + PWR_CR3_OFF;

        io_setbits32(cr3, PWR_CR3_VBE);

        if (fdt_getprop(fdt, node, "st,vbat-charge-1K5", NULL))

            io_setbits32(cr3, PWR_CR3_VBRS);

    }

Configurable in the DT

Add VBAT charge static configuration from the pwr regulator

device-tree node.

- st,enable-vbat-charge is used to enable charge

- st,vbat-charge-1K5 is used to enable fast charge with 1500 Ohms.

You may try to set it at optee board level in the "&pwr_regulators" node

Regards,

Olivier

[PatrickF]

Notice that this 'charge' is intended for an external SuperCap on VBAT (to avoid need for an external diode+resistor), must not be used with Lithium Coin-cell or any kind of rechargeable battery.

As written in product reference manual, the 'charge' resistor is automatically disconnected in absence of VDD.

Regards.

[Dat Tran]

Thank you. Yes we are using SupperCap.

Following code above, only enable charge, do we need to stop charging? what if the cap is full?

[PatrickF]

Hi,

no need to disable as capacitor charge current will null when its voltage is equal to VDD.

No risk of 'overcharge' a capacitor (it's not a battery).

Just need to enable charge resistor on each cold boot (as PWR_CR3 register is not saved in VBAT), but this is already the case if selected in DeviceTree as listed above.

Regards.

[Dat Tran]

yes, thank you a lot for this information.