Driving D+ or D- when VBUS is not powered

[Ed LeBeau]

HI,

We are looking to multiplex a few I/O on the NRF52840 to save pin count on a header.  If D+ or D- get driven when VBUS is unpowered, will that damage the NRF52840? Or if D+ is driven to VCC when VBUS is unpowered will it be not damaged? 

Thanks,

Ed

[Simonr]

Hi Ed

I'm afraid this is not a good idea. There are parasitic diodes from D+/- to DECUSB. When VBUS is not connected, DECUSB is soft clamped to VSS, and it won't be acceptable to force D+/- high when VBUS is not connected.

Best regards,

Simon