USB current limit when phone off
andy at openmoko.com
Thu Feb 5 17:34:11 CET 2009
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Somebody in the thread at some point said:
| | So normally, quitting Android it should have stick to 100mA max ?
| | And what about battery max current charge (the setting that was
| | recently made writable) ? Should it persist on shutdown too?
| Yes, the settable charge current that Balaji added sticks in "off" under
| the same rules as the charging enable action, it's only lost in PMU
| NOPOWER when there's no charger power, no battery power and even no
| backup battery power.
I'm wrong about this: it's true for charger enable and other charger
settings, but it's not true for USB current limit. That's reset in PMU
standby, which is what happens when we have any power but go "off".
And, it's reset to the variant default, which in our case is 500mA. So
it explains the problem when you consider we leave the charging limit at
1A for all modes and rely on the USB current limit to set the correct
overall consumption through USB.
We can work around it by setting the charger unit charge limit (MBCC5)
at the same time and to the same amount as the authorized USB limit in
This will fix it because although then the USB input is allowed to pull
an illegal 500mA, the rest of the board stuff at VB_SYS is OFF, so if we
limited the charger to 100mA before, 100mA is all it will eat even when
off and allowed to eat 500mA.
Balaji I know you're busy this week so I'll give it a try here.
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