AN2857

Power management tips

Doc ID 15241 Rev 3

29/31

6

Power management tips

6.1

Rules to help minimize power consumption

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Switch off all unused peripherals (peripherals are switched off by default except the

USART, LINUART and SWIM) and use the PCG feature (through the CLK_PCKENRx

registers) to disable the clock provided to the unused peripherals (the clock is provided

by default). Refer to Section 3.2: Clock configuration and power management for more

details.

●

In run mode, if the size of a loop is smaller than the size of a block, the loop code must

be located in one block.

●

All unused port pins should be configured as output low level. Do not leave any unused

I/O pin configured as a floating input which could lead to useless high consumption.

●

Use wait mode if you need external interrupt capability in low-power mode and if some

peripherals have to remain active.

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consumed.

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Use the minimum possible frequency for your application. The eight CPU prescalers

and four HSI prescalers allow the required frequency value to be fitted to the

application.

6.2

Choosing the optimal low-power mode for an application

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Application powered by a battery where the MCU is in sleep mode most of the time:

–

If the MCU is woken up due to external events, no time tracking is necessary and

power consumption has to be as low as possible. In this case, halt mode is

advised to extend battery life as much as possible.

–

Active halt mode with AWU is advised if the application does not depend on

external events but needs a non accurate periodic wakeup.

●

Application powered by a battery where the MCU is awake most of the time:

–

Active halt mode is advised if the MCU has to perform a few periodic actions

during which no peripheral has to stay on.

–

Wait mode is advised if at least one peripheral has to stay on all the time and an

interrupt can wake up the MCU.

●

Application supplied by mains but where consumption is critical:

–

Run mode, with a clock prescaler adapted to the application requirement, is

advised if the MCU has to run all the time.