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BQ76940: BMS of a battery pack

Kaustubh Kulkarni
Intellectual 1040 points
Part Number: BQ76940
Other Parts Discussed in Thread: BQ78350-R1, BQ78350

Hello all,

A customer ask,

" we need assistance for a BMS of a 11S1P battery pack where the BQ78350-R1 and BQ76940 are used.
1. When Cell UnderVoltage flag (CUV) is set, the battery seems to distort the following I²C transaction. as soon as this bit is cleared (e.g. we set the CellUndervoltageRecoveryThreshold to a lower value) the I²C bus does work. Something inside BQ78350 behaves different when this flag is set - what and why???
2. We modified the RSOC TerminateCharge (TC) Thresholds to 85% (clear) and 90% (set) - why does it disable the charge mosfet when charging is interrupted a short time. Although CellOverVoltage (COV) threshold is not reached and battery should still be able to be charged. Isn't the RSOC calculation only used for indication - not for safety protections?? Can we disable that? An untrained battery may have an RSOC of anything, but should still be able to charge until the charger circuit determines the CCCV & Timing end condition. "

Could anyone help me with this please?

Thank you

  • 0
    TI__Guru 54715 points
    Hi Kaushubh,
    The user should not talk to the bq76940 on I2C if the bq78350-R1 is used. The bq78350-R1 will set all registers in the bq76940 and will go into a recovery mode if it finds a register changed. Also there is no moderation for the bus and collisions may occur between the 2 hosts. If the user is only observing the bus, note that the state of the gauge is different, so communication may have changed.
    The part does have an option to turn off the FETs on overcharge and that is likely set by default. See the technical reference manual for how to turn off this option so that the system will reach charge termination.
    I will transfer the post to the gauge forum for any further clarification on the bq78350-R1.