Hello,
- We're using a bq2000T-based circuit to charge a 1600 mAh 3-series-cell NiMH battery pack. I've attached a schematic. Not that it matters, but in case anyone asks, the input power BAT_BOOST is from a 6 V boost converter.
- Even though the sense resistor is 50 milliohms, we fast-charge at between 800 and 900 mA. We're not sure why we're not at 1 amp, but that's a separate question. Charge termination is dT/dt.
- The problem is shown by the red trace in the attached graph; we're seeing this in a small percentage of board/battery combos. The traces are battery temperature vs. time for a four board/battery combinations, plus ambient. The red trace exhibits a failure to terminate charge. Instead, it continues to charge until the hot-temperature limit is tripped, and then the temperature drops until it gets cool enough to try to charge again, etc.
- We have a theory that we may need to increase the charge current somewhat. We have heard that dT/dt termination relies on a fast-charge current above 0.5 C.
What advice do you have?
Thanks,
Scott
