Power management tips

AN3147

20/25

DocID17035 Rev 3

5

Power management tips

5.1

Choosing the optimal low-power mode for your application

Different low power modes can be selected depending on your application:



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. Then, Halt mode is advised to

extend battery life as much as possible.

–

Active-halt mode with AWU/RTC clocked by the LSI is advised if the application

does not only depend on external events, but needs a non accurate periodic

wakeup. The LSE can be used to achieve a high timing precision.



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 remain enabled.

–

Wait mode is advised if at least one peripheral has to remain enabled all the time

and an interrupt or event 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 and low power modes cannot be used.

5.2

GPIO initialization

By default, the I/Os are configured as floating input.

It is important to change the configuration of all I/Os that are not connected to defined logic

signals so as to obtain one of the following configurations:



input configuration with pull-up



or, output configuration with a low (or high) logic level

Otherwise, an increased consumption is generated by noise, as the internal Schmitt triggers

detecting this noise are toggling.

Floating I/Os could generate additional consumption in the range of a few 10 µA.

There are also parts with some unbonded I/Os (typically different packages of the same

product). Those I/Os are connected to a defined level by factory option configuration, unless

otherwise specified in the datasheet.