Wake up from deep sleep using LPCOMP

[Judge]

Hi everyone, I have the following problem: I want to use LPCOMP to wake the nrf52840 from a deep sleep so how should I use it?

[Dmitry]

Hi,

You can look at lpcomp example in SDK. CPU will wake up on configured event (see NRFX_LPCOMP_CONFIG_DETECTION in sdk_config.h) Though this example doesn't put CPU in sleep, you can replace main loop code with __WFE() instruction to fix this:

    while (1)
    {
        __WFE();
    }

[Judge]

Hi dmitry, I have read about that example, but the problem I want to pose is that after a period of deep sleep for example 5s LPCOMP has to wake up the CPU automatically but as far as I know when the CPU sleeps, there is almost no timer. Which activity should I do?

[Dmitry]

I didn't get your case... you want to wake up by timer or by LPCOMP event?  To wake up after 5s, you can set up RTC - it can count while CPU sleeps, and then wake up CPU by compare event.

[Judge]

Hi dmitry, But as far as I know RTC does not work in system_off mode so how can I use RTC?

[Dmitry]

Yes, in system-off mode you can wake up only by GPIO or LPCOMP event. To use RTC, you have to put CPU into sleep mode. With RTC wakeup enabled, power consumption in sleep mode will be about 1.5 uA. If it's too high for you, there are external RTC chips with very low power consumption (less than 500 nA) that can wake up nRF using GPIO DETECT event.