AN2857 datasheet(27/31 Pages) STMICROELECTRONICS

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AN2857

Power consumption and wakeup time measurements and results

Doc ID 15241 Rev 3

27/31

Observations

●

When fast clock wakeup is enabled, wakeup time always equals HSI wakeup time

because the MCU automatically wakes up on HSI.

●

When the wakeup clock is the HSE crystal, wakeup time is very long and depends on

the supply voltage and the crystal used. This is due to the stabilization time of the

oscillator. This long wakeup time can be avoided by:

–

Using the fast clock wakeup feature.

–

Programing a shorter stabilization time in the HSECNT option byte (refer to the

option bytes section of the STM8S and STM8A datasheets). By default, a delay of

2048 oscillator cycles is inserted before the clock signal is released (the default

value of 2048 oscillator cycles is used in the above measurements).

●

Data for ‘HSE crystal/Flash on’ are not given in Table 12 because the wakeup time of

the Flash is always the same. The wakeup time of the Flash is about 2 µs.

●

The wakeup time of the MVR is about 50 µs.

5.2.5

Wakeup time results in halt mode

Observations

●

The wakeup time of the Flash is about 2 µs (the same as for active halt mode).

●

The wakeup time in halt mode (LPVR) is shorter than in active halt mode (see

Table 12). Note that the data in Table 12 include one AWU clock cycle sampling delay.

Table 13.

Wakeup time results in active halt mode (LPVR)

Symbol

Parameter

Condition

VDD = 3.3 V

(1)

The minus sign (-) indicates that the wakeup time is the same for VDD = 5 V.

VDD = 5 V Unit

Clock

Others

tWU(AH)

Wakeup

time from

active halt

mode

HSI

(16 MHz)

Flash on

µs

Flash off

Table 14.

Wakeup time results in halt mode (LPVR)

Symbol

Parameter

Condition

VDD = 3.3 V

VDD = 5 V Unit

Clock

Others

tWU(H)

Wakeup

time from

halt mode

HSI

(16 MHz)

Flash on

µs

Flash off

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