STM32U575 Power consumption Differences in LL_PWR_SHUTDOWN_MODE with/without RTC

[zafersn]

Hi,

I tested shutdown mode by using CubeMX applicaiton of PWR_ModesSelection on stmu575ziq dev board with configs of rtc enabled & disabled. It is clear to see that there is at least 0.3uA difference in current consumption between these two configs.

on the other hand, I tested the shutdown mode with sample app on zephyr and the power consumption result was equal to the result when I ran PWR_ModesSelection app's shutdown mode with rtc enabled.

So, for test reasons, I disabled LSE oscillator in zephyr\soc\arm\st_stm32\stm32u5\poweroff.c and it worked. I had a low power consumption result, like I had when I ran PWR_ModesSelection app's shutdown mode with rtc disabled.

/* Disable LSE oscillator */
    RCC_OscInitStruct.PLL.PLLState   = RCC_PLL_NONE;
    RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_LSE;
    RCC_OscInitStruct.LSEState       = RCC_LSE_OFF;
    if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
    {
      return SYSTEM_ERROR;
    }

Can anyone shed some light on this point to see if this is a miss configuration or if there is another reason to keep lse oscillator enabled?