How to wakeup the nRF52480 on USB power up event from sleep/low power mode?

[tordown97]

I'm using a custom battery operated board with the nRF52840, when there is no GPIO events for a specified time period, the device goes to a hibernate mode using the __WFE, to save battery power.

Im trying to figure out the best way to wakeup the device from low power mode when user connects a powered USB cable. 

My thought is to disable the USB peripheral from sleeping while entering the low power mode and use nrf_drv_power_usbevt_init() to enable the interrupts on power events, and use that to wake up the device if the event == NRFX_POWER_USB_EVT_DETECTED.

Is it the ideal way? I believe this will work but increase the sleep power consumption, is there any better work arounds?

Thanks

[Jørgen Holmefjord]

Hi,

Do you require the device to stay in System ON/__WFE mode? It is possible to wake the chip from the lowest power mode (System OFF) by both GPIO and from detecting a valid USB voltage on the VBUS pin. Wakeup from System OFF will cause the chip to reset, and you need to do any initialization again. See USB supply for more information about how this works.

If you want to stay in System ON mode, the method you describe would be the best option.

Best regards,
Jørgen

[tordown97]

Hi,

Yes I need to go back to __WFE after a status LED is lit if the USB is plugged in and I want to avoid a chip reset.

Also, to make nrf_drv_power_usbevt_init() to capture NRFX_POWER_USB_EVT_DETECTED the USB peripheral should be enabled before entering the __WFE right?

Thanks

[Jørgen Holmefjord]

It is recommended to not enable the USBD peripheral until after the VBUS voltage have been detected. See USBD power-up sequence.