Too high current draw in shutdown mode

[minded]

I'm just getting started with my STM32WB15CC nucleo board, and my first goal was to put in shutdown mode to check the current draw, which I expected to be around 1 uA. I'm measuring the current on the JP3 header with a joulescope which should represent the actual current used by the MCU itself.

I'm using the PWR_LPSLEEP example in the CubeMX IDE, and exchanged the "entersleepmode" call to the "enter shutdown mode", see below:

/* Enter Sleep Mode, wake up is done once User push-button (SW1) is pressed */

//HAL_PWR_EnterSLEEPMode(PWR_LOWPOWERREGULATOR_ON, PWR_SLEEPENTRY_WFI);

HAL_PWREx_EnterSHUTDOWNMode();

After the shutdown call, the joulescope shows a current draw of 42 uA, which seems very high for shutdown mode.

Am I missing something? Any pointers?

The reason I want to start with this basic test is because the project I'm working on is for a battery driven sensor, so a low current is crucial.

[Andrew Neil]

Make sure you've disconnected all connections to the ST-Link - leakage there could easily account for 40uA...

Check the schematics very carefully for any other possible leakage paths.

You may need to power cycle - not just reset - after using the debugger/programmer ...

[minded]

I'm using USB-C only, can I still disconnect ST-Link in that case, or is not needed then?

I also tried to put the device in shutdown from an application built with Arduino-IDE and the "low power" library. And this seems to work - I get about 1 uA current draw in shutdown.

[minded · Accepted solution]

By examining and copying the code used in the STM32LowPower Arduino library from the STM32duino core, I found the issue. What was missing was to enter shutdown mode on the radio core of the STM32WB15CC:

LL_C2_PWR_SetPowerMode(LL_PWR_MODE_SHUTDOWN);

/**
* @brief Set Low-Power mode for CPU2
* @rmtoll C2CR1 LPMS LL_C2_PWR_SetPowerMode
* @PAram LowPowerMode This parameter can be one of the following values:
* @arg @ref LL_PWR_MODE_STOP0
* @arg @ref LL_PWR_MODE_STOP1
* @arg @ref LL_PWR_MODE_STOP2 (*)
* @arg @ref LL_PWR_MODE_STANDBY
* @arg @ref LL_PWR_MODE_SHUTDOWN
*
* (*) Not available on devices STM32WB15xx, STM32WB10xx, STM32WB1Mxx
* @retval None
*/
__STATIC_INLINE void LL_C2_PWR_SetPowerMode(uint32_t LowPowerMode)
{
  MODIFY_REG(PWR->C2CR1, PWR_C2CR1_LPMS, LowPowerMode);
}

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