STM32L021D4 datasheet(14/114 Pages) STMICROELECTRONICS

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Functional overview

STM32L021x4

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DocID027982 Rev 5

Functional overview

3.1

Low-power modes

The ultra-low-power STM32L021x4 supports dynamic voltage scaling to optimize its power

consumption in Run mode. The voltage from the internal low-drop regulator that supplies

the logic can be adjusted according to the system’s maximum operating frequency and the

external voltage supply.

There are three power consumption ranges:

•

Range 1 (VDD range limited to 1.71-3.6 V), with the CPU running at up to 32 MHz

•

Range 2 (full VDD range), with a maximum CPU frequency of 16 MHz

•

Range 3 (full VDD range), with a maximum CPU frequency limited to 4.2 MHz

Seven low-power modes are provided to achieve the best compromise between low-power

consumption, short startup time and available wakeup sources:

•

Sleep mode

In Sleep mode, only the CPU is stopped. All peripherals continue to operate and can

wake up the CPU when an interrupt/event occurs. Sleep mode power consumption at

16 MHz is about 1 mA with all peripherals off.

•

Low-power run mode

This mode is achieved with the multispeed internal (MSI) RC oscillator set to the low-

speed clock (max 131 kHz), execution from SRAM or Flash memory, and internal

regulator in low-power mode to minimize the regulator's operating current. 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 to minimize the regulator’s operating current. In Low-power sleep

mode, both the clock frequency and the number of enabled peripherals are limited; a

typical example would be to have a timer running at 32 kHz.

When wakeup is triggered by an event or an interrupt, the system reverts to the Run

mode with the regulator on.

•

Stop mode with RTC

The Stop mode achieves the lowest power consumption while retaining the RAM and

PLL, MSI RC, HSE and HSI RC oscillators are disabled. The LSE or LSI is still running.

The voltage regulator is in the low-power 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, the

processor can serve the interrupt or resume the code. The EXTI line source can be any

GPIO. It can be the PVD output, the comparator 1 event or comparator 2 event

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