Vsys when given 3.3V transfusion

Andy Green andy at openmoko.com
Wed Jul 2 10:50:42 CEST 2008

Hash: SHA1

Somebody in the thread at some point said:
| 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.

The picture attached shows what happens on Vsys when it succeeds to boot
because I gave it the "3.3V transfusion" from another A5.  The blue
trace is 3.3V.

For the first 30us we draw the crazy current, but then the load seems to
reduce before Vsys is drained down far enough to make an emergency
transition to SAVE.  Then for the next 300us we complete the regulator
startup with USB able to provide enough power to additionally bring Vsys
back up to 5V.

- -Andy
Version: GnuPG v1.4.9 (GNU/Linux)
Comment: Using GnuPG with Fedora - http://enigmail.mozdev.org

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