Backup battery discharged -> GTA01 and GTA02 dead

Rod Whitby rod at
Sat Jul 19 15:53:24 CEST 2008

Andy Green wrote:
> 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).

OK, thanks.  I'll try "jump-starting" the backup battery tomorrow and 
see if I can get a boot that way.

What's the normal voltage of the backup battery?  (i.e. what should it 
charge up to?)

> | 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...

I'll try a 1.5V dry cell in parallel with the backup battery tomorrow to 
see if that will jump-start things.  Once I have a good boot I'll leave 
it on the wall charger to see if the backup battery recharges ok.

Thanks for your help, Andy.

-- Rod

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