Normal power consumption of STM32WB55 series in stop2 mode and how to make sure Core2 is not messing it up

[XB1]

Hello everyone,

We're trying to achieve a low power consumption on a custom board which have a MCU from the STM32WB55 range. I think that I was able to get into stop2 mode as PC was way lower than in sleep mode, and the device could not be detected anymore by the debugger. I reset C2BOOT bit early in main loop and I'm hoping that this Core is effectively halted, even though I don't know how to monitor it on this particular setup.

The problem is that PC is still as high as 900µA, which is A LOT compared to what I've seen most of the time on the forums for others MCUs (2µA). Does anyone know what should be the normal PC if the MCU was not on a custom board (i.e. what is the "real" PC of the STM32WB55 in stop2 mode with no peripherals enabled) in order to know if the problem may be on the board that draws a lot of current ? And how can I be sure that Core2 is halted ? Stop2 mode shouldn't be achievable with C2 running (another state than CSTOP, if I understand correctly), and I think that I achieved it, but I want to make sure that it's the case.

Have a good evening.

[Remy ISSALYS]

Hello,

According to the datasheet DS11929, the typical current consumption for Stop2 mode is 1.85µA (see table 23). You can look PWR_STOP2_RTC example which show how to enter in Stop 2 mode and wake-up from this mode using an external reset or RTC wakeup timer. On STM32WB, both CPU1 and CPU2 must be in low-power mode to set the entire System in low-power mode, corresponding to the deepest low-power mode possible. For example, CPU1 in Stop2 mode and CPU2 in Shutdown mode will make system enter in Stop2 mode. If you don't need CPU2, you have to call the following function as it's done in the example:

LL_C2_PWR_SetPowerMode(LL_PWR_MODE_SHUTDOWN);

Else, you the CPU2 is started, there is nothing to do to manage low power mode of CPU2, the CPU2 is autonomous.

Best Regards