--- In Philip Heron <> wrote:
> On Fri, 2005-06-10 at 18:25 +0000, Jesse Off wrote:
> > the device itself and are in-effect somewhat violating max current
> > draw on the USB device, if only for a few microseconds.
>
> Is there any risk to the board?
>
Not really. There is a circuit that keeps the board and CPU safely in
reset while the voltage isn't at a precise 5V. Even if you short
power and ground on the USB connector, the board won't be affected.
Since a short will draw a huge amount of current momentarily, your 5V
power supply will inevitably dip. Within a few microseconds of your
power supply dipping the board will put itself in reset and within 10
or so milliseconds the USB polyfuse will kick in, cutting off power
through the USB. Once the power supply restabilizes at 5V the board
will release reset and go through a normal bootup even with the power
supply shorted across the USB power pins. If your power supply is
strong enough to source current through a short for a few
milliseconds, your board may not even reset.
This kind of stuff usually isn't good for power supplies though... ;-)
//Jesse Off
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