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BQ27421-G1: How to choose the correct Taper Rate

Felix Neumann
Prodigy 70 points
Part Number: BQ27421-G1

Regarding to SLUUAH7B TaperRate = DesignCapacity/(0,1*TaperCurrent). Also a tolerance of 15% is added to the Taper Current in the example.

My charger theoretically quits at 13,3 mA. Logs of the Fuel Gauge show a minimal AverageCurrent of 17 mA before dropping to zero.

I've tested Taper Rate = 96 and 75. At both values the SOC reaches 100 % to early while charging. At Taper Rate = 96 the SOC reaches 100 % around 15 minutes before the charging current drops to zero. At Taper Rate = 75 this seems to happen even earlier.

How do I choose the Taper Rate correctly?

  • 0
    TI__Guru** 103395 points

    Hello Felix,

    If you decrease the TaperRate parameter this will increase the actual taper current (from the formula) so it is expected that it would happen earlier in the charge.

    There's not an ideal way to set the TaperRate, it should be set so that before the charger cuts the taper and finishes charge the gauge detects full charge. By reviewing the log I would set it around 120s before the charge stops, see where the current is and use that for your taper current.

    Sincerely,

    Wyatt Keller