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bq27210 lower capacity measurement capability

Seetharam
Prodigy 220 points
Other Parts Discussed in Thread: BQ27210, BQ27421-G1

my requirement is to monitor 72mAh battery.

1) can i use bq27210 as battery monitoring chip?

2) if yes what would be EEPROM configuration in order to work properly.

3) what would be the sense resistor values?

  • 0
    TI__Genius 14985 points

    If you just want to coulomb count and not perform gauging, then follow the instructions in SLUA347

    You should use a large sense resistor value if your currents will be very small.  The input offset of the coulomb counter is +/-15uV, so you would probably want your smallest measured signal to be at least 10x that.

    So 150uV / 10mohms = 15 mA as a minimum current to reliably measure. 

    100mohms gets you to 1.5 mA, but then you have to worry about your insertion loss if you will have high current pulses.

    If your currents are so tiny that coulomb counting isn't reliable, then you could consider using a full Impedance Track gauge like bq27421-G1 or bq27425-G2 or bq27620 which will eliminate the coulomb counter error periodically by using highly accurate voltage measurements of the battery to update the state of charge as the battery slowly discharges.  If you really need to save power for extremely long battery run-times, then consider shutting down the gauge (with either the SHUTDOWN command for bq27421 or the CE pin of the bq27520) for most of the time, then enable the gauge and wait for it to initialize to read state of charge and other registers for brief moments periodically or when necessary.  For best accuracy, try to keep current to a minimum during initialization, although the gauge can still compensate for current that is flowing.