Appendix C STM32 microcontrollers power consumption parameters

This section provides an overview on how to use STM32CubeMX Power Consumption Calculator.

Microcontroller power consumption depends on chip size, supply voltage, clock frequency and operating mode. Embedded applications can optimize STM32 MCU power consumption by reducing the clock frequency when fast processing is not required and choosing the optimal operating mode and voltage range to run from. A description of STM32 power modes and voltage range is provided below.

C.1 Power modes

STM32 MCUs support different power modes (refer to STM32 MCU datasheets for full details).

C.1.1 STM32L1 series

STM32L1 microcontrollers feature up to 6 power modes, including 5 low-power modes:

  • Run mode

This mode offers the highest performance using HSE/HSI clock sources. The CPU runs up to 32 MHz and the voltage regulator is enabled.

  • Sleep mode

This mode uses HSE or HSI as system clock sources. The voltage regulator is enabled and the CPU is stopped. All peripherals continue to operate and can wake up the CPU when an interrupt/event occurs.

  • Low- power run mode

This mode uses the multispeed internal (MSI) RC oscillator set to the minimum clock frequency (131 kHz) and the internal regulator in low-power mode. The clock frequency and the number of enabled peripherals are limited.

  • Low-power sleep mode

This mode is achieved by entering Sleep mode. The internal voltage regulator is in lowpower mode. The clock frequency and the number of enabled peripherals are limited. A typical example would be a timer running at 32 kHz.

When the wake-up is triggered by an event or an interrupt, the system returns to the Run mode with the regulator ON.

  • Stop mode

    This mode achieves the lowest power consumption while retaining RAM and register contents. Clocks are stopped. The real-time clock (RTC) an be backed up by using LSE/LSI at 32 kHz/37 kHz. The number of enabled peripherals is limited. The voltage regulator is in low-power mode.

    The device can be woken up from Stop mode by any of the EXTI lines.

  • Standby mode

This mode achieves the lowest power consumption. The internal voltage regulator is switched off so that the entire V CORE domain is powered off. Clocks are stopped and the real-time clock (RTC) can be preserved up by using LSE/LSI at 32 kHz/37 kHz.

STM32 microcontrollers power consumption parameters

RAM and register contents are lost except for the registers in the Standby circuitry. The number of enabled peripherals is even more limited than in Stop mode.

The device exits Standby mode upon reset, rising edge on one of the three WKUP pins, or if an RTC event occurs (if the RTC is ON).

Note: When exiting Stop or Standby modes to enter the Run mode, STM32L1 MCUs go through a

state where the MSI oscillator is used as clock source. This transition can have a significant impact on the global power consumption. For this reason, the Power Consumption Calculator introduces two transition steps: WU_FROM_STOP and WU_FROM_STANDBY . During these steps, the clock is automatically configured to MSI.

C.1.2 STM32F4 series

STM32F4 microcontrollers feature a total of 5 power modes, including 4 low-power modes:

  • Run mode

    This is the default mode at power-on or after a system reset. It offers the highest performance using HSE/HSI clock sources. The CPU can run at the maximum frequency depending on the selected power scale.

  • Sleep mode

Only the CPU is stopped. All peripherals continue to operate and can wake up the CPU when an interrupt/even occurs. The clock source is the clock that was set before entering Sleep mode.

  • Stop mode

This mode achieves a very low power consumption using the RC oscillator as clock source. All clocks in the 1.2 V domain are stopped as well as CPU and peripherals. PLL, HSI RC and HSE crystal oscillators are disabled. The content of registers and internal SRAM are kept.

The voltage regulator can be put either in normal Main regulator mode (MR) or in Lowpower regulator mode (LPR). Selecting the regulator in low-power regulator mode increases the wake-up time.

The flash memory can be put either in Stop mode to achieve a fast wake-up time. or in Deep power-down to obtain a lower consumption with a slow wake-up time.

The Stop mode features two sub-modes:

  • Stop in Normal mode (default mode)

In this mode, the 1.2 V domain is preserved in nominal leakage mode and the minimum V12 voltage is 1.08 V.

  • Stop in Under-drive mode

In this mode, the 1.2 V domain is preserved in reduced leakage mode and V12 voltage is less than 1.08 V. The regulator (in Main or Low-power mode) is in under-drive or low-voltage mode. The flash memory must be in Deep-power-down mode. The wake-up time is about 100 µs higher than in normal mode.

  • Standby mode

This mode achieves very low power consumption with the RC oscillator as a clock source. The internal voltage regulator is switched off so that the entire 1.2 V domain is powered off: CPU and peripherals are stopped. The PLL, the HSI RC and the HSE crystal oscillators are disabled. SRAM and register contents are lost except for registers in the backup domain and the 4-byte backup SRAM when selected. Only RTC and LSE oscillator blocks are powered. The device exits Standby mode when an external reset (NRST pin), an IWDG reset, a rising edge on the WKUP pin, or an RTC alarm/ wake-up/tamper/time stamp event occurs.

  • VBAT operation

    It allows to significantly reduced power consumption compared to the Standby mode. This mode is available when the VBAT pin powering the Backup domain is connected to an optional standby voltage supplied by a battery or by another source. The VBAT domain is preserved (RTC registers, RTC backup register and backup SRAM) and RTC and LSE oscillator blocks powered. The main difference compared to the Standby mode is external interrupts and RTC alarm/events do not exit the device from VBAT operation. Increasing VDD to reach the minimum threshold does.

C.1.3 STM32L0 series

STM32L0 microcontrollers feature up to 8 power modes, including 7 low-power modes to achieve the best compromise between low-power consumption, short startup time and available wake-up sources:

  • Run mode

This mode offers the highest performance using HSE/HSI clock sources. The CPU can run up to 32 MHz and the voltage regulator is enabled.

  • Sleep mode

This mode uses HSE or HSI as system clock sources. The voltage regulator is enabled and only the CPU is stopped. All peripherals continue to operate and can wake up the CPU when an interrupt/event occurs.

  • Low-power run mode

This mode uses the internal regulator in low-power mode and the multispeed internal (MSI) RC oscillator set to the minimum clock frequency (131 kHz). In Low-power run mode, the clock frequency and the number of enabled peripherals are both limited.

  • Low-power sleep mode

This mode is achieved by entering Sleep mode with the internal voltage regulator in low-power mode. Both the clock frequency and the number of enabled peripherals are limited. Event or interrupt can revert the system to Run mode with regulator on.

  • Stop mode with RTC

The Stop mode achieves the lowest power consumption with, while retaining the RAM, register contents and real time clock. The voltage regulator is in low-power mode. LSE or LSI is still running. All clocks in the V CORE domain are stopped, the PLL, MSI RC, HSE crystal and HSI RC oscillators are disabled.

Some peripherals featuring wake-up capability can enable the HSI RC during Stop mode to detect their wake-up condition. The device can be woken up from Stop mode by any of the EXTI line, in 3.5 µs, and the processor can serve the interrupt or resume the code.

  • Stop mode without RTC

This mode is identical to “Stop mode with RTC “, except for the RTC clock which is stopped here.

  • Standby mode with RTC

The Standby mode achieves the lowest power consumption with the real time clock running. The internal voltage regulator is switched off so that the entire V CORE domain STM32 microcontrollers power consumption parameters

is powered off. The PLL, MSI RC, HSE crystal and HSI RC oscillators are also switched off. The LSE or LSI is still running.

After entering Standby mode, the RAM and register contents are lost except for registers in the Standby circuitry (wake-up 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), an IWDG reset, a rising edge on one of the three WKUP pins, RTC alarm (Alarm A or Alarm B), RTC tamper event, RTC timestamp event or RTC wake-up event occurs.

  • Standby mode without RTC

This mode is identical to Standby mode with RTC, except that the RTC, LSE and LSI clocks are stopped.

The device exits Standby mode in 60 µs when an external reset (NRST pin) or a rising edge on one of the three WKUP pin occurs.

Note: 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.

C.2 Power consumption ranges

STM32 MCUs power consumption can be further optimized thanks to the dynamic voltage scaling feature: the main internal regulator output voltage V12 that supplies the logic (CPU, digital peripherals, SRAM and flash memory) can be adjusted by software by selecting a power range (STM32L1 and STM32L0) or power scale (STM32 F4).

Power consumption range definitions are provided below (refer to STM32 MCU datasheets for full details).

C.2.1 STM32L1 series features three VCORE ranges

  • High performance Range 1 (VDD range limited to 2.0-3.6 V), with the CPU running at up to 32 MHz

The voltage regulator outputs a 1.8 V voltage (typical) as long as the V DD input voltage is above 2.0 V. Flash program and erase operations can be performed.

  • Medium performance Range 2 (full VDD range), with a maximum CPU frequency of

16 MHz

At 1.5 V, the flash memory is still functional but with medium read access time. Program and erase operations are still possible.

  • Low performance Range 3 (full VDD range), with a maximum CPU frequency limited to

4 MHz (generated only with the multispeed internal RC oscillator clock source)

At 1.2 V, the flash memory is still functional but with slow read access time. Program and erase operations are no longer available.

C.2.2 STM32F4 series features several VCORE scales

The scale can be modified only when the PLL is OFF and when HSI or HSE is selected as system clock source.

  • Scale 1 (V12 voltage range limited to 1.26 - 1.40 V), default mode at reset.

HCLK frequency range = 144 MHz to 168 MHz (180 MHz with over-drive).

This is the default mode at reset.

  • Scale 2 (V12 voltage range limited to 1.20 - 1.32 V).

HCLK frequency range is up to 144 MHz (168 MHz with over-drive).

  • Scale 3 (V12 voltage range limited to 1.08 - 1.20 V), default mode when exiting Stop mode.

HCLK frequency ≤120 MHz.

The voltage scaling is adjusted to f HCLK frequency as follows:

  • STM32F429x/39x MCUs:

    • Scale 1: up to 168 MHz (up to 180 MHz with over-drive) – Scale 2: from 120 to 144 MHz (up to 168 MHz with over-drive) – Scale 3: up to 120 MHz.

  • STM32F401x MCUs:

No Scale 1

  • Scale 2: from 60 to 84 MHz – Scale 3: up to 60 MHz.

  • STM32F40x/41x MCUs:

    • Scale 1: up to 168 MHz

    • Scale 2: up to 144 MHz

C.2.3 STM32L0 series features three VCORE ranges

  • Range 1 (VDD range limited to 1.71 to 3.6 V), with CPU running at a frequency up to

32 MHz