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STM32 Low-power modes


Overview​

HW: STM32L053

Power consumption range​

  • Range 1: VDD 1.71 ~ 3.6, CPU up to 32 MHz
  • Range 2: full VDD range, CPU up to 16 MHz
  • Range 3: full VDD range, CPU up to 4.2 MHz

Modes​

  • Sleep
    • Only the CPU is stopped.
    • All peripherals continue to operate.
    • All peripherals can wake up the CPU when an interrupt/event occurs.
    • Power consumption at 16 MHz is about 1 mA with all peripherals off.
  • Low-power run
    • is achieved with
      • MSI RC oscillator set to the lowspeed clock (max 131 kHz),
      • execution from SRAM or Flash memory,
      • internal regulator in low-power mode.
  • Low-power sleep
    • is achieved by entering Sleep mode with the internal voltage regulator in low-power mode.
    • All I/O pins keep the same state as in Run mode.
    • When wakeup is triggered by an event or an interrupt, the system reverts to the Run mode with the regulator on.
  • Stop mode
    • achieves the lowest power consumption while retaining the RAM and register contents and real time clock.
    • All clocks in the Vcore domain are stopped.
    • The PLL, MSI RC, HSE crystal and HSI RC oscillators are disabled.
    • The LSE or LSI is still running.
    • The voltage regulator is in the low-power mode.
    • All I/O pins keep the same state as in Run mode.
    • Some peripherals featuring wakeup capability can enable the HSI RC during Stop mode to detect their wakeup condition.
    • The device can be woken up from Stop mode by any of the EXTI line, in 3.5 µs. It can be
      • any GPIO EXTI.
      • the PVD output.
      • the comparator 1 event or comparator 2 event (if internal reference voltage is on)
      • the USB/USART/I2C/LPUART/LPTIMER wakeup events.
      • the RTC alarm/tamper/timestamp/wakeup events if with RTC.
  • Standby mode
    • is used to achieve the lowest power consumption.
    • The internal voltage regulator is switched off so that the entire Vcore domain is powered off.
    • The PLL, MSI RC, HSE crystal and HSI RC oscillators are also switched off.
    • The LSE or LSI is still running if with RTC.
    • The RAM and register contents are lost except for registers in the Standby circuitry (wakeup logic, IWDG, RTC, LSI, LSE Crystal 32 KHz oscillator, RCC_CSR register)
    • The device exits Standby mode in 60 µs when
      • an external reset (NRST pin)
      • a rising edge on one of the three WKUP pins
      • an IWDG reset if with RTC
      • RTC alarm (Alarm A or Alarm B), RTC tamper event, RTC timestamp event or RTC Wakeup event occurs, if with RTC
caution

The RTC, the IWDG, and the corresponding clock sources are not stopped automatically by entering Stop or Standby mode.The LCD is not stopped automatically by entering Stop mode.

Standby with RTC Alarm​

Pinout & Configuration​

  • Timer
    • RTC
      • Mode
        • Activate Clock Source
        • Activate Calendar
        • Alarm A -> internal Alarm A
      • Configuration
        • Parameter Settings
          • General -> Asynchronous Predivider value = 124
          • General -> Synchronous Predivider value = 295
          • 37 KHz / (124 + 1) / (295 + 1) == 1 (Depend on clock source)
        • NVIC Settings
          • RTC global interrupt -> Enable

Clock Configuration​

Set RTC clock.

Example​

rtc.c

...

void MX_RTC_Init(void)
{
    ...

    /* USER CODE BEGIN Check_RTC_BKUP */
    if(HAL_RTCEx_BKUPRead(&hrtc, RTC_BKP_DR0) == 0x1234) return;

    ...

    HAL_RTCEx_BKUPWrite(&hrtc,RTC_BKP_DR0,0x1234);
    /* USER CODE END Check_RTC_BKUP */

    ...
}

...

main.c

...

/* USER CODE BEGIN PV */
RTC_TimeTypeDef sTime;
RTC_DateTypeDef sDate;
RTC_AlarmTypeDef sAlarm;
/* USER CODE END PV */

...

int main(void) {

    ...

    /* USER CODE BEGIN 2 */
    // Check the Standby flag
    if(__HAL_PWR_GET_FLAG(PWR_FLAG_SB) != RESET) {
        // Clear the Standby flag
        __HAL_PWR_CLEAR_FLAG(PWR_FLAG_SB);
        printf("Wake up from standby mode\n");
    } else {
        printf("Power on or Reset\n");
    }

    // Clear the Wake Up flag
    __HAL_PWR_CLEAR_FLAG(PWR_FLAG_WU);

    HAL_RTC_DeactivateAlarm(&hrtc, RTC_ALARM_A);
    /* USER CODE END 2 */

    ...

        if(condition) {
            HAL_RTC_GetTime(&hrtc, &sTime, RTC_FORMAT_BIN);    // BIN
            // Must call HAL_RTC_GetDate() after HAL_RTC_GetTime()
            HAL_RTC_GetDate(&hrtc, &sDate, RTC_FORMAT_BCD);    // BCD

            // Set to compare only seconds
            sAlarm.AlarmTime.Seconds        = (sTime.Seconds + 5) % 60;
            sAlarm.AlarmTime.SubSeconds     = sTime.SubSeconds;
            sAlarm.AlarmTime.SecondFraction = sTime.SecondFraction;
            sAlarm.AlarmMask          = RTC_ALARMMASK_ALL & ~RTC_ALARMMASK_SECONDS;
            sAlarm.AlarmSubSecondMask = RTC_ALARMSUBSECONDMASK_SS14_3;
            sAlarm.Alarm              = RTC_ALARM_A;
            HAL_RTC_SetAlarm_IT(&hrtc, &sAlarm, RTC_FORMAT_BIN);

            printf("Try to enter standby mode\n");

            HAL_PWR_EnterSTANDBYMode();
            printf("Failed to enter Standby mode\n");
        }

    ...
}

...


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