Open-Drain output connected to WKUP pin

[Adam Mitchell]

Hi,

I'm working with an STM32L073RZ on a custom board, using MbedOS 5.12.0 bare metal. The board is a very low power weigh scale that is normally in Standby mode and is awoken by an accelerometer (connected to PC_13), an NFC chip (connected to PA_0). Specifically, the NFC chip is an M24SR64-YMN6T/2 with the GPO connected to PA_0. or an RTC event. The accelerometer and RTC wake the processor just fine - it's the NFC chip that I'm having an issue with.

If I disconnect the NFC's GPO from the WKUP pin then my current consumption sits at around 10µA (which is what I'm expecting), however as soon as I connect the GPO to a WKUP pin my current consumption skyrockets to ~200µA. I've tried connecting the GPO to both WKUP pins and the behaviour is the same. I've tried with and without pullup resistors on the GPO line and still get the same result.

Any insights as to what might be going on would be greatly appreciated.

Thanks,

Adam

[waclawek.jan]

Is the GPO pin of NFC chip active, i.e. low, when the consumption is high? Is the WKUP pin's internal pullup switched on?

JW

[Adam Mitchell]

Hey JW,

Current consumption is high both when the GPO line is high and low with no difference between them. The internal pullup isn't switched on - the WKUP pin is in it's default state (weak pull down) when attempting to enter Standby mode.

Cheers,

Adam