We have been using the BQ2040 in a handheld computer for battery management with a 2-cell 18650 pack for many years with good results.
We have recently tried to change from using Molicell (MicroSun) 2400mAh cells to a Sanyo 2600mAh pack but have found problems with recalibrating.
The Molicell EDV1 and EDVF were both set to 6000mV and reliably calibrates after a qualified discharge to cut-off point. With the Sanyo however, we do not get a recalibration occurring after a similar discharge. We noticed that the Sanyo voltage starts dropping rapidly from around 6800mV so increased EDF1 to 6800 and EDVF to 6400.
If we allow the pack to discharge to below EDV1 but then start charging before it reaches EDVF, the calibration DOES take place so it seems the fact that it runs to cutoff point is the issue.
I understand the following reasons could nullify a "qualified discharge", none of which seem to be the case:
1. Full charge capcity at start of cycle.
I assume we are there. FCC and DESCAP are both initialised to 2400 mAh and we charge to 8400mV till current drops below 120mA.
2. >256mV step at EDV1 threshold
Drop is around 40mV per minute around the EDV1 threshold
3. Charging (>10mAh) during discharge cycle.
There is no charging taking place.
4. Low Temp fault flag set.
Temperatures are being reported around 38 C throught the discharge (nowhere near 12)
What other reasons could there be for not regarding this as a "qualified discharge"? Could it be related to the charge cycle thereafter? Do we need to start at a lower charging current (we currently charge at 650mA until CHGV)
Thanks,
Lester