Connecting USB VBUS to 5V power rail

[DemoniacMilk]

What happens if the USB PHYs VBUS is directly connected to +5V instead of the USB Jack? Is the device just always powered, or does this have any side effects (e.g. device is powered -> expects to be connected -> enters some weird, undefined state)?

[mon2]

http://www.xcore.com/forum/viewtopic.ph ... hilit=vbus

[DemoniacMilk]

Thank you for bringing that topic to my attention, but to be honest: I do not understand what they are saying.

[mon2]

Believe the summary is that if you use an external power supply for the Vbus rail (and not the Vbus from the USB connector) then you are 'self powered'. The issue you may face is that if the host PC enters sleep mode and then wakes up, your USB product may not be detected unless you power cycle the computer and your USB product. This will be a real pain for the end users.

See here:

http://www.xcore.com/forum/viewtopic.ph ... =USB+sleep

VBUS is required to detect disconnect / connect conditions.

For the USB Audio boards by XMOS:

That board was only designed to work via bus power

Perhaps someone from XMOS can confirm this summary ?