USB, Toshiba

Scott Allen mlxxxp-Re5JQEeQqe8AvxtiuMwx3w at public.gmane.org
Thu Jan 20 12:03:33 UTC 2011


On 19 January 2011 14:52, Lennart Sorensen <lsorense-1wCw9BSqJbv44Nm34jS7GywD8/FfD2ys at public.gmane.org> wrote:
> Well one usb 2 connector may be used to provide 500mA if the device asks
> for it from the controller.  Without asking, 100mA is the max a device
> may use.

Does anyone here know if /how this is physically enforced? Do
motherboards, hubs and other USB hosts actually have two stage current
limiting circuitry, or will they always provide the maximum current
(possibly protected with a thermal fuse or other current limiter) even
if not negotiated?

I bet many of the USB gadgets and toys that use the interface strictly
for power don't do any power negotiation and may not even have data
lines connected. In this case, do they limit themselves to 100mA?

-- 
Scott A.
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