Question about charging

[Werner Almesberger]

Helge Hafting wrote:
> According to documentation, the freerunner wants 100mA, 500mA or 1000mA, 
> and no more than 5V. Limiting to 5V should be easy enough. I just wonder 
> if the charging can handle unstable voltage, for example if it 
> alternates between useable 5V and "too low" 10 times a second.

The PMU may be able to keep up with this, but I'm not sure the
battery will like it. If you google for "short charge cycles", you
find claims that this kills Li-Ion batteries.

In particular, if you look at page 84 of
http://people.openmoko.org/tony_tu/GTA02/datasheet/PMU/PCF50633UM_6.pdf
you see that dropping below the USB detection threshold (~4V) will
reset the charger state machine and thus defeat the mechanism that
avoids trickle-charging the battery when it's full.

Harald posted a while ago that such trickle-charging changes the
battery's chemistry and damages it.

- Werner