STM8S datasheet(104/467 Pages) STMICROELECTRONICS

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Power management

RM0016

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DocID14587 Rev 14

Main voltage regulator (MVR) auto power-off

By default the main voltage regulator is kept on Active-halt mode. Keeping it active ensures

fast wakeup from Active-halt mode. However, the current consumption of the MVR is non-

negligible.

To further reduce current consumption, the MVR regulator can be powered off automatically

when the MCU enters Active-halt mode. To configure this feature, set the REGAH bit in the

Internal clock register (CLK_ICKR) register. In this mode:

•

The MCU core is powered only by the LPVR regulator (same as in Halt mode).

•

Only the LSI clock source can be used, as the HSE clock current consumption is too

high for the LPVR.

The Main voltage regulator is powered on again at wakeup and it requires a longer wakeup

time (refer to the datasheet electrical characteristics section for wakeup timing and current

consumption data).

Fast clock wakeup

As described for Halt mode, in order to get the shortest wakeup time, it is recommended to

select HSI as the fMASTER clock source. The FHWU bit is also available to save switching

time.

A fast wakeup time is very important in Active-halt mode. It supplements the effect of CPU

processing performance by helping to minimize the time the MCU stays in Run mode

between two periods in low power mode, and thus reduces the overall average power

consumption.

Since the clock is not automatically switched to the original master clock, the application

must restore the clock source before entering Halt/Active-halt mode as soon as it is ready.

10.3

Additional analog power controls

10.3.1

Fast Flash wakeup from Halt mode

By default the Flash is in power-down state when the microcontroller enters Halt mode. The

current leakage is negligible, resulting in very low consumption in Halt mode. However the

Flash wakeup time is relatively slow (several µs).

If you need the application to wakeup quickly from Halt mode, set the HALT bit in

Section 4.8.1: Flash control register 1 (FLASH_CR1). This ensures that the Flash is in

Standby mode when the microcontroller enters in Halt mode. Its wakeup time is reduced to a

few ns. However, in this case the consumption is increased up to several µAs.

Refer to the electrical characteristics section of the datasheet for more details.

10.3.2

Very low Flash consumption in Active-halt mode

By default, in Active-halt mode, the Flash remains in operating mode to ensure the fastest

wakeup time, however in this case the power consumption is not optimized.

To optimize the power consumption you can set the AHALT bit in Flash control register 1

(FLASH_CR1). This will switch the Flash to power-down state when entering Active-halt

mode. The consumption decreases but the wakeup time increases up to a few µs.

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