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

Andy Green andy at openmoko.com
Fri Apr 18 09:07:06 CEST 2008

Hash: SHA1

Somebody in the thread at some point said:
| 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!

Guys did we secretly understand this problem and I missed it?

Something horrible happens to a low percentage of RT9711 Vin protection
circuit in the factory.  Maybe the unknown "something horrible" comes
and attacks PMU USB pins if we just 0R out the RT9711 and pass it on.

I understand the redesign aspect to get rid of the RT9711 and it sounds
like a cool idea (if we are sure it is good for all cases like
charger)... but we only examine this situation because of chips blowing
up connected to that net, and we don't know why and we cannot reproduce
it here AFAIK.

If we make the change we just hope that somehow the PMU USB inputs are
less sensitive than the RT9711 without actually understanding what makes
the problem.  Hey we can still do it but that is the case I think.

- -Andy
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