I intend to develop a battery monitoring system for a friend's project. He will have 4 or 5 large lithium iron phosphate cells in series to power his stuff for three days or so, and he wants to be able to monitor the charge level, polling the battery monitor from a nearby USB port. Also the monitoring circuit should provide a signal when the battery gets empty (maybe full too). I'm looking for suggestions regarding initial design decisions such as what IC to use to monitor state of charge.
I've read a little bit of background material, but haven't really started. My friend suggests that we probably want to go with a chip with LiFePO4 fuel gauge functionality built in, for increased accuracy and decreased development time. He suggested the
BQ78350-R1 from TI, but I am not sure. That chip is intended to work with a companion chip they are calling an "analog front end," to monitor the actual voltage level on each cell and provide balancing to the pack. But it's designed for small cells. The ones my friend intends to use are large ones, rated for a maximum charge and discharge current of 130 amps.
So it seems I would have to build a custom circuit to take the place of the analog front end chip, and I'm thinking it might be better to start off with a different IC altogether. But the other thing I am thinking is that the balancing may only matter during charging, and perhaps if pack balancing is not needed during discharge, then my circuit doesn't even need to have that functionality. Apparently my friend already has a charger with cell balancing built in.