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Enable USB in firmware on PCB without USB connector

pkrn

Hi there,

we are working on a number of nRF52840-based hardware products with almost identical functionality. Some have USB and BLE connectivity, while others offer BLE connectivity only. We want to run the same firmware on all PCBs. Our approach is to differentiate between PCBs only when absolutely necessary, for instance when outputting model names. Can we also follow this approach when it comes to USB, i.e. can the USB drivers be enabled on boards where the USB pins are grounded/floated/whatever? (The hardware design of the non-USB boards is not finalized yet, so we are flexible in this regard.) If so, is there any recommendation how we should connect the unused USB pins?

Thanks,
Philip

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  • +1

    There is no problem to initialize the USB driver, even though there is no USB attached at any time. From the USB supply chapter you can find: "When VBUS rises into its valid range, the software is notified through a USBDETECTED event. A USBREMOVED event is sent when VBUS goes below its valid range. Use these events to implement the USBD start-up sequence described in the USBD chapter." In your case there will never be a USBDETECTED event, so even though USB driver is initialized, it will never do anything without this event.

    In terms of schematic and layout I suggest to use the layout that at any time most closely to your hardware configuration:
    https://infocenter.nordicsemi.com/topic/ps_nrf52840/ref_circuitry.html 

    Kenneth

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  • +1

    There is no problem to initialize the USB driver, even though there is no USB attached at any time. From the USB supply chapter you can find: "When VBUS rises into its valid range, the software is notified through a USBDETECTED event. A USBREMOVED event is sent when VBUS goes below its valid range. Use these events to implement the USBD start-up sequence described in the USBD chapter." In your case there will never be a USBDETECTED event, so even though USB driver is initialized, it will never do anything without this event.

    In terms of schematic and layout I suggest to use the layout that at any time most closely to your hardware configuration:
    https://infocenter.nordicsemi.com/topic/ps_nrf52840/ref_circuitry.html 

    Kenneth

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