Backup battery discharged -> GTA01 and GTA02 dead

Andy Green andy at
Sat Jul 19 15:49:12 CEST 2008

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Somebody in the thread at some point said:

| Are you 100% sure that a good backup battery level is not required for
| boot on a GTA02v5?  Who can answer that for GTA01Bv4?

Well, I have booted devices with very low backup battery level, during
the time we hunted down the reason for this
no-boot-with-low-or-no-battery issue I did check the battery state.  And
according to pcf50633 documentation, the effect of backup battery level
is mainly to act as a gateway into NOPOWER state of the PMU, which is
where we are at after manufacture anyway (and we evidently booted at
that time).

| Is there an easy way that I can test my theory that a dead backup
| battery causes a dead device?  Is there a test point on the GTA02 I can
| look at to debug whether the PMU is powering up the device or not?

VB_SYS which shows how you're doing on with this "trap" issue is under
the main "can" unfortunately.

| Is there a safe way to recharge the backup battery in-circuit using
| external means when it's voltage is this low and the device refuses to
| power-on?
| If the battery cannot be easily recharged, what is the exact type of
| battery used for the backup battery, and how is it attached to the board
| (it seems to be soldered in) - what is the easiest way to detach or
| desolder the current battery and install a new one?

No it is rechargeable and is trickle-charged by the PMU during
operation.  If I wanted to do what you want, I would desolder the
battery and then drive that signal from somewhere else, like IO_3V3 via
a resistor.  But my comfort level about trashing things is a bit higher
than a customer's...

- -Andy
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