AN4102

Managing power consumption in automotive applications

Doc ID 023129 Rev 1

13/16

For instance, if one estimates the power consumption of an STM8AL MCU in the active

the HSI oscillator), this corresponds to:

If the microcontroller were to be always active, the current consumption would be constant

and equal to 4 mA. The example above shows that the average current consumption is 40

times lower (4 mA vs. ~100 µA) in this operating mode and yet the microcontroller is active

approximately a hundred times per second, which may be sufficient depending on the

considered application. The microcontroller’s time activity represents about 25 ms over a 1-

second operating time (2.5%). If the microcontroller needs more activity time, then the

active/idle ratio can be adapted. Similarly, increasing the clock speed when possible is a key

factor to shorten the time spent in the active mode and then decrease the global power

consumption of the system.

On the other hand, when there is no activity required until one event happens, as for

instance, a switch that has to be operated before the application performs a series of

actions, then the MCU can be placed in low-power mode until an external event is detected

(external interrupt, peripheral interrupts, etc…). This mode is ideal in terms of energy saving

but may not be convenient in the case where high security is required, for example, when

the system needs to regularly control that the microcontroller is present and able to perform

any action at any time.

STM8AL automotive low-power microcontrollers allow various configurations that can

enable users to tune their products according to the application requirements. It is advised

to follow the power management recommendations outlined in the STM8L and STM8AL

application note (AN3147).