D+ and D- signals before power supply of the chip

[Konrad S]

The device i am currently developing is a battery powered dongle with internal power supply unit for battery charging.
I am using nrf5340 USB pins D+ and D- for communication.

There is a case in which the battery is dead (nrf5340 not powered) and plugging the USB would put voltage on D+ and D- before the battery charger wakes up and charge all capactiors accross VCC/VDDH/VBUS pins. 

Is that situation a potential risk for nrf5340 or the USB module is physicaly switched off unless VBUS is present?

[Turbo J]

The USB data lines D+ and D- are pulled down by the USB host when no device was detected on a port. I don't see a risk here.

[ketiljo]

VBUS only power the USB-PHY. there's no risk to back power the rest of the device if only VBUS is present.