mcxn236 usb device mode without VBUS

[allu]

Hi NXP,

We refer NXP SDK_2_14_0_FRDM-MCXN236_rfp USB device example to develop a USB device. However, is it possible to make the USB device mode work without VBUS?

If yes, how can we modify this in the SDK?

Thanks,

Alan

[diego_charles]

Hi @allu 

Thank you very much for your patience.

As I reviewed internally, please find below our feedback. 

We strongly suggest customers to link MCX N2xx's USB_VBUS pin with USB connector as recommended in our  hardware design guide and  implemented in the official FRDM-MCX N 236 schematic.  

With the USB_VBUS pin detect, the application firmware can easily know  if the USB is attached or not.

Leaving USB_VBUS  floating is possible, but require the software  skip the attach detection, and use a software state machine to check if the USB is linked or not. But we are not sure about the workload to implement this.

Additonally, leaving USB_VBUS disconnect may impact on the USB certification attach and de-attach test, but it will not impact on other test items. As mentioned before, you may use the software approach to solve the attach and de-attach test item issue, but it is not our recommendation. 

Anyway, we strongly suggest you to enable the USB_VBUS.

Thank you, 

Diego