System Off mode and powered peripherals

RE: System Off mode and powered peripherals

Andrea Verdecchia — Fri, 01 Nov 2024 14:10:02 GMT

Thanks

RE: System Off mode and powered peripherals

Priyanka — Fri, 01 Nov 2024 13:57:48 GMT

That's right. So when the nRF52 chip is in System Off mode, GPIO configurations are preserved, including any pull-up or pull-down settings. But, the chip enters an extremely low power state where most functionality is powered down.

So even if a GPIO pin has a pull-up configured, it will not draw significant additional current beyond the chip's specified System Off current consumption. You can take a look at this ticket.

-Priyanka

RE: System Off mode and powered peripherals

Andrea Verdecchia — Fri, 01 Nov 2024 10:51:09 GMT

Thank you for the clarification.

[quote userid="107729" url="~/f/nordic-q-a/115729/system-off-mode-and-powered-peripherals/508732"]The best is to put all GPIOs in disconnected input (default state).[/quote]

So, if I put the chip in System Off mode and the GPIO pin is disconnected, will that pin not draw any current even if there's a pull-up on it?

RE: System Off mode and powered peripherals

Priyanka — Thu, 31 Oct 2024 21:44:52 GMT

Hi Andrea,

[quote user="Thoraz"]In this case, the code, before activating the system_off mode, only configures the interrupt on the pin for wake-up and disables the UART (for the console) by calling the function pm_device_action_run(cons, PM_DEVICE_ACTION_SUSPEND). [/quote]

Yes that's right. This is done to reduce power consumption, as the UART peripheral can contribute significantly to idle current.

[quote user="Thoraz"]However, on the development board, if I understand the schematic correctly, the nRF52840 chip remains connected via UART to the nRF5340 interface chip, which stays active. In this case, is there any problem,[/quote]

That's also right. This connection will not be a problem for the system_off mode of the nRF52840, because when it enters system_off mode, it will shut down most of its circuitry, including the UART peripheral, so the physical connection to the interface chip won't cause any issues or prevent the nRF52840 from entering its lowest power state. But please see here that UART is an exception that needs to be handled explicitly by the application for power management.

[quote user="Thoraz"]In my case, the only bus that would remain active on my nRF52840 in system_off mode would be an I2C that has pull-ups on the VDD power supply. The active peripheral would still be a slave, and since the SDA and SCL signals are open-drain on the ports of my sleeping nRF52840, I would only have a pull-up to VDD. Could this be a problem?[/quote]That should be fine then. If the other device is a slave, it will not do anything unless it receives an I2C command, which it will not receive if the nRF is in system off.
But keep in mind that you may want to disable the peripheral to save power. High impedance pins doesn't draw a lot of power (but more than nothing). The best is to put all GPIOs in disconnected input (default state).

Hope this helps :)

Regards,

Priyanka

RE: System Off mode and powered peripherals

Andrea Verdecchia — Wed, 23 Oct 2024 07:53:47 GMT

Hi Priyanka,
I still have a couple of questions:

I am looking at the Zephyr example on the system_off mode, which is compatible with the nRF52840 DK development board. In this case, the code, before activating the system_off mode, only configures the interrupt on the pin for wake-up and disables the UART (for the console) by calling the function pm_device_action_run(cons, PM_DEVICE_ACTION_SUSPEND). However, on the development board, if I understand the schematic correctly, the nRF52840 chip remains connected via UART to the nRF5340 interface chip, which stays active. In this case, is there any problem, or am I missing something?
In my case, the only bus that would remain active on my nRF52840 in system_off mode would be an I2C that has pull-ups on the VDD power supply. The active peripheral would still be a slave, and since the SDA and SCL signals are open-drain on the ports of my sleeping nRF52840, I would only have a pull-up to VDD. Could this be a problem?

I hope I explained myself well.

RE: System Off mode and powered peripherals

Priyanka — Tue, 22 Oct 2024 20:28:58 GMT

Hi Andrea,

When in system_off mode, the internal circuitry of the chip aims to minimize the power consumption and the pins will be in a high-impedance state. So in case you connect them to powered peripherals and they transmit data, this can cause anomalous behaviour and also possible current leakage due to the high-impedance. Sometimes this can also cause backfeeding from the powered peripherals to the chip and can cause problems since the chip would be in partial operation in the system_off state. So it would be better to not connect them to powered peripherals. In case it's unavoidable, then maybe you could add some external protection circuit or even series resistors before connecting them to the powered peripherals.

Regards,

Priyanka