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BQ78PL114: BMS IC (or concept) for LiFePo, 180A, 4 cell, SOC+SOH and active balancing mandatory (similar BQ78PL114)

Karl Dietmann
Prodigy 20 points
Part Number: BQ78PL114
Other Parts Discussed in Thread: BQ40Z50, , BQ76920, BQ78350

Hi there,

I am looking for a BMS-IC that can handle 4 LiFePo cells (4s1p) with a total capacitiy up to 180Ah with CC and DCC up to 180A. Active balancing is mandatory as well as SOC and SOH  (via I2C/SMB/SPI/... interface).

I came across the BQ78PL114S12 which seems to a nearly perfect fit, except for the current range of 110A which is stated in the datasheet's front page. We need the ability of discharge of 180A for at least 10 minutes while maintaining correct SOC readings.

So bascially I am looking for a IC or combination of ICs (might be a gas-gauge + protection IC for SOC+SOH plus additional ICs for active balancing) for LiFePo chemistry.

Is it suitable to use active balancing ICs in addition to a passivly balancing BMS-IC?

Thank you very much

Karl

  • 0
    TI__Genius 10370 points

    Karl,

    I am sad to say TI does not offer another solution for active cell balancing. For a 4S design our flagship bq40z50 is the best device I can recommend, but it uses passive cell balancing and a bleed off resistor. 

    With capacities so high we can "Fake" the gauge to divide the currents by 10 to make the gauge stay within the correct operation range. You can also use external balancing FETS to increase the balancing current. 

    Thanks,

    Eric Vos

  • 0 in reply to Vos
    Prodigy 20 points

    Hi Eric,

    thank you so much for your answer. For the sake of my understanding:

    - It is a "way to go" to 1/10th the current sense resistor and thus multiply current-related measurement *10 in software (bq40z50) ?

    - Isn't that an option for the BQ78PL114, too? (R_sense/5) If not could you quickly outline why?

    - Do you see any problems in using BQ78350 + BQ76920 in our application (LiFePo,4s, 180A, 180Ah)

    Again thank you,

    Karl

  • 0 in reply to Karl Dietmann
    TI__Genius 10370 points

    Karl,

    Yes you basically apply 10A current, but tell the gauge it's 1A when calibrating. Yes all gauges should have that option. The issue is the bq78pl114 is such an old device we cant really support it. We still sell it for people who are in production already and just continue to use it. So any support needs.

    the bq78350/bq76920 should work, but it again is not Active cell balancing. 

    Thanks,

    Eric Vos