AN3404

Power consumption factors

Doc ID 018847 Rev 3

5/30

Consequently, power consumption depends on:

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The microcontroller unit (MCU) chip size

This includes the technology used, the number of transistors, and the analog

features/peripherals embedded and used in the application.

●

The MCU supply voltage

The amount of current used in CMOS logic is directly proportional to the square of the

power supply voltage (V²). Thus, power consumption may be reduced by lowering the

MCU supply voltage. This is less critical for STM8TL5xxx devices than for other

microcontrollers, as an internal voltage regulator is used. However, the MCU supply

voltage could have an impact on the remaining components on the board.

●

The clock frequency

Power consumption may be reduced by decreasing the clock frequency when fast

processing is not required by the application.

●

The number of active peripherals or MCU features used (such as timers,

communication peripherals, watchdogs, ProxSense, etc.)

The greater the number of active peripherals or features, the greater the amount of

power consumed.

●

The operating mode

Power consumption depends on which mode a particular application is running

(example: central processing unit (CPU) on/off, oscillator on/off). For an application

powered by a battery, the consumption is very important. Usually, the average

consumption should be below a certain target value to ensure an optimum battery

lifetime. This means that an application can consume more for short periods of time

and keep its average current consumption below the target value.