Charge complete detection?

Hi,

I've recently updated my phone to support battery monitoring. The
only thing left for basic PDA functionality on HTC Apache is battery
charge support.

I know how to charge the battery -- I've identified the AC detect
GPIOs and the charge enable GPIOs. However, I'm not sure when
charging should be considered complete. I want to avoid over-charging
batteries, so until I've figured this out I'm planning on disabling
the charger.

I'm writing this email to solicit feedback from other phone developers
on how they handle the charge complete sequence.

The HTC Apache phone does not appear to have a w1 bus. Instead it
looks like it uses a simple ADC chip (the ad7877) to monitor battery
voltage and current. In WinCE, five values are read every 10 seconds
- they appear to be: voltage, current, charge voltage?, temperature,
and an unknown value. The "charge voltage" is non-zero only when the
charger is enabled, and as a guess it represents the negative
potential between the battery leads. Finally the last unknown value
seems very constant (perhaps it is an internal core voltage).

When charging, the normal battery voltage appears to be always around
4.2 volts. However, I've seen WinCE do a "trick" where it disables
the charger for 10ms and then senses the battery voltage again. It
seems to do this more frequently as it "completes" the charge
sequence.

I've also noticed that even after WinCE reports that the battery is
fully charged, if the AC is left in, it will occasionally re-enable
the charger for brief periods (without reporting that it is). As a
guess, the phone may run off of the battery even when AC is present,
and the software periodically recharges to account for recent losses.

Any thoughts? Any references I can research?
-Kevin
Received on Wed Dec 27 2006 - 19:05:15 EST