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From: Andrew Jackson on 22 Apr 2010 03:23
On 21/04/2010 19:35, linsky wrote:
> Hi I'm a new USB port designer. I am wondering that if my board do not need
> the USB host to supplier voltage through USB port. Should I need to
> supervise and protect the VBUS for overcurrent? Thanks!

Well if you aren't supplying VBUS then clearly you can't detect over
current!

The USB 2.0 specification requires that a root port (i.e. host) must
supply either one unit load (low power) or five unit loads (high power)
(see 7.2.1). Externally powered hosts need to supply five or more unit
loads.

So you should add over-current protection if you are making a USB host.
Most (stand-alone) chips provide suitable inputs/outputs to manage this.

There are other considerations if you are developing an OTG host.

Andrew
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