Enabling USB communication

Question

To be able to have USB communication/interface, do I need to apply 5V to VBUS? Or will 3V on Vdd be enough. I am planning to use coin cell that is max rated for 4.2V so it won't be able to provide 5V.

awneil · Answer

Dan Colob said: I am planning to use coin cell that is max rated for 4.2V so it won't be able to provide 5V 
 But the USB itself will provide 5V - surely? 
 Dan Colob said: do I need to apply 5V to VBUS? 
 Have you read the USB section in the Product Specification? 
 https://infocenter.nordicsemi.com/topic/ps_nrf52840/usbd.html?cp=4_0_0_5_34 
 eg, 
 "The signal pins and the pull-up will operate only while VBUS is in its valid voltage range" 
 " The physical layer interface (PHY)/USB transceiver is powered separately from the rest of the device (VBUS pin)" 
 "Enable USBD after VBUS has been detected only" 
 etc, ...

awneil · Answer

If it doesn't have a USB cable connected, there's no point in enabling the USB - is there?! 
 And when there is a USB cable connected - it gives you the 5V !