I am in the process of developing a battery charger for Li-ion, NiCad, and NiMH battery chemistry. I wanted to include gas gauge functionality into the charger, but was unclear as to what my available options and corresponding best choice would be. One complication is that the batteries are composed of 4 series stacked cells, but the charger only has access to the serial terminal voltage, and not the individual cell voltages. I was thinking about using the BQ20Z65-R1 for its accuracy with Li-Ion, but wasn't sure if this could also be used with the other chemistries, or how he performance would be if the individual cells are not monitored. If this is not a good option, it appears I would have to use a multi-chem chip like the bq2060A. Any advice in this area is appreciated.
The best option for your requirements is the bq2060A. The bq20z65-R1 is for LION chemistries and it needs access to the individual cells. The bq2060A can gauge nickel and lead acid chemistries, and it can work with just pack level access.
Thanks for the response. I did have one more question. If I decided to use the bq20z65-R1 for the Li-Ion batteries only, are you saying the chip would not work because there is no access to the individual cells? What if the chip was wired up such that the chip saw 4 individual cell voltages, they were just always balanced (due to a simple voltage divider across the main terminals). Would the impedance track gas gauge work in this case?
It wouldn't work. The cell balancing FETs are internal to the device itself, so you need real cells hooked up to each connection. There isn't a way to disable balancing. The algorithm also relies on accurate cell voltage measurements (<2mV error per cell). Obviously by dividing the voltage down you're going to introduce quite a bit of error into the measurement itself.
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