General power management tips

AN3404

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Doc ID 018847 Rev 3

5

General 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:

●

Applications 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. Halt mode is advised to extend

battery life as much as possible.

–

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

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

●

Applications 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 using

no peripheral except the ProxSense.

–

Wait mode is advised if at least one peripheral should be enabled all the time and

an interrupt or event can wake up the MCU.

●

Applications 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

●

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.

In 28-pin packages, the unbounded I/Os are connected to a defined level by factory option

configuration.

In 20-pin packages, the following pins PA6, PA7, PD2, PD3 and PD7 must be configured in

output push-pull low level by the application code in order to avoid extra consumption on

these unbounded pins.