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Original question:

BQ76940: ambient temperature setting for of CEDV gas gauge calibration

BQ76940: Definition of 0% and 100% SOC and temperature reading of CEDV gas gauge

Niels van Sadelhoff
Prodigy 30 points
Part Number: BQ76940
Other Parts Discussed in Thread: BQ78350-R1

Hello,

I have 2 questions regarding the CEDV gas gauge calibration:

1. How are 0% and 100% SOC defined by the algorithm? I assume that the configuration file parameter "CellTermV" will determine 0% SOC, is this correct? Will the algorithm assume that the battery is at 100% SOC at the beginning of each continues discharge test?

2. To my understanding the chip can take up to 3 external thermistor measurements. Which of these signals will be used for the calculation of the gas gauge? Or will an average be used? I'd like to know in order to determine which data to use for the temperature columns of the configuration file.

Thank you.

  • 0
    TI__Guru* 81034 points

    Hi Niels,

    For CEDV gauges, coulomb counting is used to track charge in and out of the battery. This tracks the remaining capacity and SOC.

    There are different options for the BQ78350-R1 (companion gauge for the BQ76940) to define the SOC behavior at the point of valid charge termination. These bits (CSYNC and RSOCL) are described in section 5.3 of the BQ78350-R1 Technical Reference Manual.

    At the end of discharge, the behavior is different. There are 3 end-of-discharge voltages defined that typically correspond to 7%, 3%, and 0% SOC. These can be fixed or compensated for load and temperature. These are fully described in Chapter 9 of the BQ78350-R1 TRM.

    Regarding the external thermistors, the DA Configuration register in the BQ78350-R1 selects whether to use the average temperature from the 3 thermistors or the maximum temperature reported. 

    Best regards,

    Matt