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BQ24171 Recharge Threshold

Jeremy51164
Intellectual 780 points
Other Parts Discussed in Thread: BQ24171, BQ24172

Hello,

I am using the BQ24171 for a three series cell LiFePO4 battery pack, with termination voltage of 3 x 3.6V = 10.8V

I understand that given the lower per-cell voltage, the hysterisis voltage sag to trigger a recharge cycle is lower than when using 4.1V LiPo's.  Does this make this charger unsuitable for use with LiFePO4 cells, due to repeated triggering of the recharge cycle?

Thank you,

Jeremy.

  • 0
    TI__Expert 3160 points

    Hi Jeremy,

    Does your application specifically need a JEITA compliant part?

    The bq24172 would be a better option because it has a charge voltage analog feedback pin (FB) in place of the fixed cell/voltage (CELL) pin that bq24171 offers. Using the bq24172, you can properly adjust the charge voltage regulation to match the termination voltage of your pack. 

    Best Regards,

    Rachel

  • 0 in reply to Rachel Moore
    Intellectual 780 points

    H Rachel,

    Thank you for your post.  I don't need JEITA specifically, but it appears that both the bq24171and bq172 can use an analog control voltage on their feedback pin, so I'm not convinced there is muc benefit in changing parts.  I think the key to avoiding shallow cycling is to use a larger recharge hysteris window, which is only 50mV for the analog configuration (Vrechg) for both parts, but over 200mV if using the digital (ternery) selection.

    After several minutes the cycling appears to stop as the cells stabilise.

    Thanks again,

    Jeremy.