Optimal way of putting nRF9160 into low power mode without shutting down the power

RE: Optimal way of putting nRF9160 into low power mode without shutting down the power

Didrik Rokhaug — Thu, 14 Jan 2021 13:17:55 GMT

What application are you running on the nRF9160?

If you are running the Serial LTE Modem, or use the AT host subsystem, you can just send the AT command, wait for the OK, then cut the power.

If not, you would need a way for STM32 to indicate that it want to turn off the nRF9160, so the application on the nRF9160 can turn off the modem. Depending on your application, this can be done over the already existing UART line, or by some other means. You should also have a way for the nRF9160 to indicate to the STM32 that the modem has turned off, as that can in some cases take some time.

RE: Optimal way of putting nRF9160 into low power mode without shutting down the power

Sid D — Thu, 14 Jan 2021 12:30:59 GMT

Thanks for your response. Yes that is correct, in our current implementation we just cut off power by disabling the buck converter.

For achieving your recommendation, the host microcontroller STM32L4 sends the AT command (AT+CFUN=0) to nRF9160 over UART before powering down the buck? The AT commands need to be initiated by the STM32L4?

RE: Optimal way of putting nRF9160 into low power mode without shutting down the power

Didrik Rokhaug — Thu, 14 Jan 2021 12:19:21 GMT

Hi,

How do you currently turn off the modem?

Do you just cut off the power?

If you instead turn off the power gracefully with AT+CFUN=0, it will store information about the currently connected network to flash, so that next time it starts, it can speed up connection significantly.

However, you still have to disconnect and re-connect to the network.

Another solution, is to use "Power Saving Mode" (PSM). This is a feature in LTE-M and NB-IoT which let's the device turn off the radio for long periods at a time, while still staying connected to the network. You can request PSM from the network with the +CPSMS AT command. If granted by the network, the device can still send data whenever it wants, but it cannot receive any data while in PSM.

When the sleep period is over (or the device initiates a transmission), the device only has to do a tracking area update, instead of a full re-attach. In addition, it will have to stay online for a short period afterwards (active time) before going back to sleep.

Best regards,

Didrik