Vsys oscillation vs 3.3V rail

Andy Green andy at openmoko.com
Wed Jul 2 08:48:45 CEST 2008

Hash: SHA1

Somebody in the thread at some point said:

| With the 1 Ohm resistor, the PMU powers off after a minute or so.
| Guess it doesn't like to share ;-)
| So it seems that stabilizing IO_3V3 alone does not solve the issue.

No it wouldn't "solve the issue", but last night it reliably caused the
A5 I tested it on here to boot without battery.  I suspect it does it by
reducing the current through Vsys enough that it defers or avoids the
overcurrent detection taking it away.

That A5, after getting the full backup battery, continued to do the
extended fast retry stuff on Vsys, to the point where sometimes after a
while it is able to spontaneously boot.  It takes about 10 goes on the
last try where it boots.  But the number of retries is extremely random
and I didn't find any clue why, I guess it is oscillation in Vsys
overcurrent action behind it.

This morning the backup battery on it was discharged, there is no
stuttering of Vsys again, so the path through pcf50633 state machine
differs as defined in the datasheet, we get push straight to SAVE and
stay there a while if there is no backup battery power: if the backup
battery is good we go to STANDBY instead I believe and can go to ACTIVE

- -Andy
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