ADC lines behavior when STM32 is not powered?

[YGehl.1]

Hi!

I'm using an ADC line of the STM32 MCU to read battery voltage that goes from 6.7V to 8.4V.

The battery voltage is given to the MCU via a divider (by 4, so the maximum voltage given to the ADC line of the MCU will be 2.1V).

I wanted to know, if there will be any issue/ damage to the MCU when it is not powered, because the ADC line gets the voltage as long as battery is connected to the PCB regardless of MCU being powered on/off.

I haven't seen any damage yet! Just asking for future purposes.

Thanks in advance!

[Ozone]

If not mistaken, there are no specifications for allowed voltages in an unpowered state.

One might assume the +-300mV as for GPIOs applies, but I remember recommendations of ST staff here to avoid such situations.

IMHO, with sufficient series resistance (as seems to be the case with your battery voltage divider) reducing the current to uA range is safe.

A common problem with external voltages through GPIOs is that they might power up the core fully or partially, leading to all sorts of strange and unsuspected behavior.