Other Parts Discussed in Thread: BQ2057, BQ24103,
My application requires a 2 cell solution (I need the 7.4 Volts). I was looking at purchasing a battery like this one. I also want to charge it through USB (5V). Thankfully, it looks like most of TI's charger ICs include a boost regulator, so that should be alright. The application will also run using a Microcontroller.
I spent a lot of time browsing the available chargers, and I'm wondering what the main difference is between the BQ240, 24103, 2412, 24133, etc.. is. They mainly seem to have the same function. The BQ2417 seems to be a little more complex, and the BQ2057 seems to have the same function, but just with less status outputs and monitors.
Overall, I think something like the BQ24103 with a CELLS setting for a 2 cell pack (which can run on 5V input voltage, right?) would be great for what I need, and it has the temperature control which is great. But then I'm unsure about which fuel gauge to use. There seem to be very few fuel gauges that measure a single 2 cell pack at 7.4 V. Most of them seem to measure it as two separate cells and look at the balance. This is an option for me too, I could purchase a version of that battery that gives me access to the midpoint. But then I'd need a charger IC that can "see" the two cells and charge/balance them separately, rather than the ones I mentioned that charge to 8.4 V as if it were a single pack. Because the balance is done by the charger IC, not the fuel gauge, correct? I see that there's a chip, the BQ40260 that does multi cell charging, balancing, and gauging. This seems like a dream chip! But it communicates using SMBus, and my microcontroller only has I2C and SPI communication. So the way I see it, I have 3 options (again, all must be able to be powered by 5V USB):
1) Find something like the BQ40260 that communicates through I2C or SPI.
2) Use something like the BQ24103 for 7.4V charging, and find a gas gauge IC (I2C) that will monitor that one pack.
3) Find a new charging chip that can balance 2 cells and then use the readily available gauges (I2C) that monitor 2 cells.
All of these options require some kind of chip that I can't find. Can I get some assistance in trying to find chips that fulfill these requirements? A couple of more novice questions:
1) Are multi-cell balancing solutions always favored over the 1 7.2 V pack style that I originally suggested?
2) When using a thermistor to monitor temperature, am I supposed to attach the thermistor directly onto the battery? Should I like get a bit of tape and literally stick it on?
3) So the gauge will send all these data about voltage and charge accumulation through I2C to my microcontroller. How do I use this information to get a final "Battery percentage charge" value? Do I need to evaluate the battery as it says here?
Thanks for any help. Maybe this was more suited towards general product support, but that part of the website doesn't seem to be working:
