STM32L4 keep pin high in StandBy mode?

[misiael]

Posted on November 03, 2017 at 17:53

Hi,

I work on design with STM32L452RET6P and I'm considering power managment. I've got some voltage regulators that needs high voltage on SHDN pin and i want to use GPIO to keep this regulators on. I have read datasheet, and i found information that in StadBy I/Os can be configured with internal pull-up, pull-down or floating. My question is: Is it enough to configure pin, pull-up,out, and set high before entry to Standby to keep this pin high during StandBy? Thank you for understending but i must be sure before design PCB. Best regards,Micha?#stm32l4 #standby

[Szymon PANECKI]

Posted on November 03, 2017 at 18:11

Hello Michal,

Thanks for your interest in STM32L4 MCUs. This is correct that in Standby mode devices from L4 series can keep internal pull-up/down resistors active for I/O pins. 

Regarding the steps, which you need to do in order to have pull-up or pull-down active in Standby mode, please find below the minimum code based on HAL:

HAL_PWREx_EnableGPIOPullUp(PWR_GPIO_A, GPIO_PIN_2); 

HAL_PWREx_EnablePullUpPullDownConfig();

HAL_PWR_EnterSTANDBYMode();

WIth above code you will configure pull-up for PA2, enable keeping this setting in Standby mode and finally enter Standby mode. No additional configuration of the pin is required.

Regards

Szymon

[Mark Shoe]

Posted on March 08, 2018 at 13:55

Bug found in STM32Cube_FW_L4_V1.11.0

The function HAL_PWREx_EnableGPIOPullUp set the bit for pull up and one line later is clears the pulldown register

SET_BIT(PWR->PUCRA, (GPIONumber & (~(PWR_GPIO_BIT_14))));

CLEAR_BIT(PWR->PDCRA, (GPIONumber & (~(PWR_GPIO_BIT_13|PWR_GPIO_BIT_15))));

There might be something wrong with the 

CLEAR_BIT construction, only SET_BIT(PWR->PUCRA, GPIO_PIN_0);

 did work for me.

[Vincent HUE]

Posted on March 08, 2018 at 17:43

Thanks Szymon for the explanation.

Does it matter if the IO was configured as output before going to standby/shutdown ?

In other word, are the CR3_APC and PUCRX/PDCRX settings only used in standby/shutdown or do we need to 'prepare' the pins (setting them as input) before using the HAL_PWREx_EnableGPIOPullUp() API ?

Cheers,

Vincent