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BQ78350: fuel gauge coulomb counter inaccuracy

Steve Coffin
Prodigy 125 points
Part Number: BQ78350

We are experiencing a lot of trouble with the fuel gauge on the BQ78350. It seems to get reset when the BMS is put into shipping mode. Do you know if TI has addressed this issue in newer firmware versions? Also even when calibrated with a full discharge it often looses its state. As it is the fuel gauge is all but useless. Is there a way to initialize the fuel gauge manually through the I2C bus?

  • 0
    TI__Guru* 80843 points

    Hi Steve,

    When you enter shipping mode, power is removed from the BQ78350-R1. This resets the device registers, so the charge tracked by the coulomb counter is reset. Parameters in data flash like Full Charge Capacity are preserved, but the immediate state of charge can only be determined from the battery cell voltages as the device powers up.

    The initial battery capacity at device reset is described in more detail in Section 9.1.4 of the BQ78350-R1 Technical Reference Manual (http://www.ti.com/lit/ug/sluubd3d/sluubd3d.pdf). In order to determine the state-of-charge, the correct ChemID must be selected for your battery. This is the only time the BQ78350-R1 uses the ChemID to determine the SOC and Remaining Capacity. The Gas Gauging section of the Using the BQ78350-R1 application report describes the process of selecting the ChemID and for configuring the gauging parameters: http://www.ti.com/lit/an/slua924/slua924.pdf 

    There is not a way to initialize state-of-charge manually. If the cell voltages have been at rest before coming out of Ship mode, the ChemID should allow the device to give a fairly accurate state-of-charge. The RemCap Initial Percent parameter can be used to adjust the initial state-of-charge value.

    Best regards,

    Matt