AN3248

Analog watchdog during Stop mode

Doc ID 17758 Rev 3

7/17

2

Analog watchdog during Stop mode

The ADC in the STM32L1 family can be used as an analog watchdog with programmable

high and low thresholds. Nevertheless, the MCU must be kept in Run mode to be able to

watch analog voltage on input since the ADC is powered off in Stop mode. For ultra low

power STM32L1 devices, two analog comparators, COMP1 and COMP2, can be combined

in window mode and used as an analog watchdog that remains powered on while the MCU

is stopped. Consequently, lower consumption is achieved and power is saved.

Figure 5 displays the configuration of two such analog comparators in window mode.

external pin PB3. The analog input voltage can be applied on group 6 of the analog switches

(PB4 or PB5).

Figure 5.

Analog comparators combined in window mode

Note:

In High-density devices, pins PB6 and PB7 can be used also as COMP2 non-inverting

inputs.

DAC_OUT1 and DAC_OUT2 cannot be used in Stop mode since the DAC peripheral is

powered off.

WNDE

PB5

Threshold2:

multiple sources

-

+

-

+

COMP1

COMP2

PB4

GR6

GR6

CMP1OUT

EXTI line 21

CMP2OUT

Wakeup

EXTI line 22

PB3

DAC_OUT1

DAC_OUT2

VREFINT

3/4 VREFINT

1/2 VREFINT

1/4 VREFINT

Input voltage

Wakeup

Threshold1:

VREFINT (1.22 V)

-1

-2

ai17494