USB-OVP

[Uwe Klein]

On 8/29/08, Joerg Reisenweber <joerg at openmoko.org> wrote:

> Nope, Tranzorb won't help here because the energy this component had to absorb
>  is too high, so it would burn out. Transzorbs are for ESD surge suppression
>  only.
Yes, but the trick is that they burn to a short circuit. You still need a fuse
element in front that burns garanteed open ( fuse, resistor )
Design target is to aim for a reasonable repair and avoid a fullbrick.

>  However meanwhile main rant here seems to be about additional cost for a
>  ~$0.05 diode to clamp reverse voltage and trip the polyfuse we have in new
>  GTA03 design. Obviously there is a notion customer wouldn't like to pay this
>  price for increased ruggedness of USB-power input. Also there have been
>  objections about the safety of such a design, not taking in account that it
>  can not be less safe than what we had originally.
>
same applies here if you use the unsymmetric variety.
Overvoltage and reverse voltage draw current through the TransZorp
long enough to have the fuse blow. Save!

A freerunner is more of a cherished posession than forex a Motorola F3 ;-)

uwe