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Best possible strategy for deep sleep and awakening

lecozahu

Hello,

I'm working on NRF9160-DK.
I would like to be able to put the card to sleep in the deepest sleep possible to be able to save as much energy as possible and to wake it up if the state of one of my 3 inputs changes (button press, accelerometer or other). What is the right strategy for falling asleep and waking up? k_sleep () or is there something better?
What orders of magnitude am I supposed to get for my NRF9160-DK in the best solution to sleep card?

Best regards,

Lecozahu

  • 0

    Hello, Lecozahu!

    It is possible to set the device in System OFF mode, being the deepest internal power saving mode. In this mode it's possible to wake the device through GPIO peripherals. However, in most cases I will recommend using power saving mode (PSM), if that is available from your network provider. This puts the modem in sleep, enabling low power operation. Interrupts can then be used to wake the device from PSM for transmissions. This blogpost may be helpful with regards to how PSM is used (there they use k_sleep()). 

    The reason I recommend PSM is that waking up from System OFF mode takes a long time, and consumes quite a lot of power as the connection to the LTE network has to be established again.

    For wake up on interrupts you can also take a look at this thread.

    The expected power consumption for the different modes are shown in the pictures below. Note that the floor current may vary with nRF9160 SiP generation and other factors.

    Modem:

    System OFF:


    Hope this is helpful!

    Best regards,
    Carl Richard

  • 0 in reply to Carl Richard

    Thank you for your help, your answer helped me a lot.
    However I still have one or two questions, can we wake up with an RTC timer in the off system? it's noted that there 'can wake up only with the GPIOs and a reset but I want to be sure. If you can't, what is the minimum level allowing a revival with an RTC timer and a GPIO interrupt? Is that PSM  ?

    Best regards,

    Lecozahu

  • +1 in reply to lecozahu

    Hello, again!

    Good to hear that the answers were helpful. In System OFF mode only Reset and GPIO can wake up the device, the RTC is unavailable. As seen in the current consumption specifications I added in my previous comments the RTC is available as a wake up source, with a resulting minimum of 2.35µA. 

    System ON mode is not to be confused with PSM, which is a feature of the modem. The current used during PSM will add to the current used by the MCU. From our tests you can expect ~7µA with PSM in combination with System ON. Note that the modem in this case maintains connection to the network, saving power and time costs when waking up. My fellow engineer, Håkon, has done a quite good explanation of the Low Power modes in this thread. 

    Hope this is helpful!

    Best regards,
    Carl Richard

  • 0 in reply to Carl Richard

    Hello !

    I forgot to answer... I'm sorry !!

    Thank you very much for your help, it helps me a lot

    Best regards

    Hugo LE COZANNET

  • 0 in reply to lecozahu

    No problem! Glad to hear that I could help!

    Have a nice weekend.

    Best regards,
    Carl Richard

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