System Power Off

RE: System Power Off

Jørgen Holmefjord — Thu, 29 Feb 2024 10:13:45 GMT

If wakeup from SystemOFF was caused by VBUS, bit "I" (0x00100000) in RESETREAS register will be set on wakeup.

RE: System Power Off

bauch2 — Thu, 29 Feb 2024 10:03:37 GMT

How can I verify if the VDD feedback to VBUS is triggering a wakeup due to the VBUS voltage exceeding the 3.4-volt range, considering the circuit configuration? dinosaur game

RE: System Power Off

hmolesworth — Tue, 13 Feb 2024 02:58:36 GMT

Actually I tried applying an NFC field to see what happens, but NFC Sense only seems to force a wakeup and reset if TASKS_SENSE is previously enabled, which is not the default (tested on nRF52832, not nRF52840).

    // This might be a secondary reset due to NFC or port io wakeup or first power-on reset
    if ((NRF_POWER->RESETREAS & 0x90000) == 0)
    {
       NRF_NFCT->TASKS_SENSE = 1;
       NRF_POWER->SYSTEMOFF = 1;
    }

Maybe on the nRF52840 the VDD feeds back to VBUS in the absence of USB and trips a wakeup if the VBUS voltage is above 3.4 volts range; depends a little on circuit configuration; easy to check by logging RESETREAS

RE: System Power Off

hmolesworth — Mon, 12 Feb 2024 19:51:36 GMT

Maybe disable the NFC pins (if enabled):

"In System OFF, the NFCT Low Power Field Detect function can wake the system up through a reset.
If the system is put into System OFF mode while a field is already present, the NFCT Low Power Field
Detect function will wake the system up right away and generate a reset"

We save the RESETREAS register before the errata are applied.

Edit: note a coil is not required for System Off reset, just a differential 1.2 volts between the 2 pins, such as a finger touch or photodiode .. might try this, be a useful feature for low-power wakeup. The NFC pins are high-impedance in System OFF; thus sensitive to noise.

RE: System Power Off

Ecic2002 — Mon, 12 Feb 2024 19:00:55 GMT

Thank you Jørgen for the response.

The system off command used in the sample is the same that I have been trying to use in code. The device does seem to power off, but then almost immediately starts back up. The VBUS pin is low, and I have both disconnected the JTAG and restarted the device. Is there a way to record what is causing the power on event? Are there any other systems similar to USB VBUS where they are enabled by default to power on the device? I have nothing in my board file setup to be a wakeup source.

RE: System Power Off

Jørgen Holmefjord — Mon, 12 Feb 2024 14:46:43 GMT

Hi,

As described in the Product specifications, wakeup from System OFF mode includes GPIO, LPCOMP, NFCT, USB or a reset. You can reference the nRF5x System Off demo sample in Zephyr on how to enter SystemOFF mode. Note that you should power cycle the board after programming, to make sure it is not in debug interface mode, which will force Emulated System OFF mode.

It is not possible to disable the USB VBUS as wakeup source, and there is no need to configure this explicitly.

Best regards,
Jørgen