USB-OVP

headers Joerg Reisenweber | 28 Aug 2008 19:27

Am Do  28. August 2008 schrieb Andy Green:
> Somebody in the thread at some point said:
> 
> | Charger Overshoot Voltage VCHGR_OVRSHT 6.0 V max.
> | -----
> |
> | Though we couldn't even attach a USB-charger compliant to this spec,
> as it has
> | to be equipped with micro-USB plug, we should expect to see voltages on
> | USB-receptacle of up to 6.0V AT LEAST.
> 
> Why?  Our charger doesn't follow that spec that mentions 6.0V.
> 
> | I think it's a strong argument for additional OVP extending our actual
> | abs.max.rating of 5.5V to limits safely beyond 6.0V, like we are actually
> | about to do for GTA03.
> 
> Regulator and cap in the charger should mitigate this.  Why don't we
> measure our actual charger performance in this case, shouldn't be too hard.

For one simple reason: USB-charging was meant to work with *any* USB-charger 
(otherwise we would have used ID-pin for VDD of charger  and Neo wouldn't 
take any power from USB-VBUS, thus no issue with OVP), and for sure we don't 
want to restrict customers to usage of OM-wallwart-powersupply only. We 
wouldn't even get away with this, legally. As long as our device has a 
USB-receptacle, it has to cope with insertion of what a customer can 
reasonably assume should work when attached to it.

Then we also got the *wide* field of externally powered hubs. Ever had a look 
at the way those are providing power to downstream-connectors? And at the 
power-supplies that are (or are not!) shipped with these hubs.
"Dear customer! There are a plethora of powered USB-hubs out there. We 
strongly recommend NOT to attach Neo to any of those, as we didn't care to 
protect the device against voltages that may be found on a lot of the cheaper 
ones you might incidentally use. Please connect Neo to the original charger 
or certified good hosts only!" 
Do we really need more reasons to care about that issue?

cheers
jOERG

Re: USB-OVP