[Fwd: Re: [gta02] Fwd: PS: high rate of broken devices even on prodction test. DESIGN BUG!]

joerg at openmoko.org joerg at openmoko.org
Fri Apr 18 07:10:20 CEST 2008

Am Fr  18. April 2008 schrieben Sie, Allen Chang:
> Dear All:
> I found that if I don't plug the USB (include D+ and D- data) , the PMU 
> setting will not change in U-Boot.
> I remove U4905 and short the U4905( RT9711)'s VIN and VOUT. I set U4904 
> (AAT1275) to output 5V.
> I set  MBCC7 =3 (suspend) and MBCC8 = 0, the total current doesn't  
> still increase
> Therefore, using 0 ohm resistor replace U4905 is maybe  a solution.

If we really can disable USB power_in on PCF50633 by setting the registers to 
appropriate value, I think we are better off without RT9711. So kick it off 
board and replace it with 0R. Fine!

If we still get problems with exploding chips, it really doesn't matter in the 
end whether RT9711 dies, or PCF50633 blows up.

However if we are going to do *any* PCB changes here, I'd strongly suggest to 
include some advanced OVP for the USB-port (maybe something around a FET with 
>50V U(d-s max), and a Zener). I feel quite uneasy with this safety headroom 
of ~1Volt before some crap charger is busting our chips.


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