USB-OVP

[Joerg Reisenweber]

Am Mi  29. Oktober 2008 schrieb silver62:
> 
> Hi,
> why there is a requirement for VCHGR_UNDSHT < 4V? If the voltage of charger
> fall below 4V when the charger is connected for 2 ms is this a big issue?
> 
> Regards,
> 
> Silvestro


I didn't write this spec ;-), but I guess it's to avoid possible oscillation 
caused by device detecting USB-removal due to Vusb < 4V and switching off USB 
power path.
Also note this is a USB2.0 complying spec, and USB2/USB-OTG uses Vusb 
modulation to signal certain status changes between host and device.

cheers
jOERG


> 
> 
> Joerg Reisenweber wrote:
> > 
> > FYI:
> > 
> > From http://www.usb.org/developers/devclass_docs/batt_charging_1_0.zip
> > 
> > -----
> > Battery Charging
> >     Specification
> >          Revision 1.0
> >           Mar 8, 2007
> > 
> > p.19:
> > If the current drawn from a USB charger changes suddenly within the range
> > of 
> > 0mA to 500mA, then the
> > transient voltage from a USB charger shall not go below VCHGR_UNDSHT.
> > Under no 
> > circumstances shall the
> > transient voltage of a USB charger exceed VCHGR_OVRSHT.
> > 
> > p.23:
> > 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.
> > 
> > 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.
> > 
> > cheers
> > jOERG
> > 
> >  
> > _______________________________________________
> > hardware mailing list
> > hardware at lists.openmoko.org
> > http://lists.openmoko.org/mailman/listinfo/hardware
> > 
> > 
> 
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> 
> 
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