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Original question:

BQ40Z50-R2: Current sense/Gas Guage

BQ76920: Companion fuel gauge bq78350 and bq34z100

Jeffrey Wright
Expert 2875 points
Part Number: BQ76920
Other Parts Discussed in Thread: BQ78350, , BQ78350-R1, BQ34Z100, BQ76930, BQ76940, BQ34110, BQ34Z100-G1

Hello;

I note that the bq78350 includes its own  AFE, ADC and Coulomb Counter, but when used as a companion to the bq76920, it seems these are not used(?). Rather, its datasheet says "The bq78350-R1 device continuously monitors the measured current and integrates the digital signal from the AFE (the bq769x) over time, using an internal counter." 

In contrast, the bq34z100's datasheet shows its "companion" controller (the NRD bq77908) also attached to the sense resistor. ??

I need the scalability featured in both gauges, but not on the 76920, and so it would seem I would need to have the gauge do the measuring.

Please clarify. Thanks

  • 0
    TI__Guru* 81034 points

    Hi Jeffrey,

    The BQ78350 does not include its own AFE with a Coulomb Counter. The BQ78350 is purely a companion controller/gauge that can be used with the BQ76920 (5S), BQ76930 (10S), or BQ76940 (15S). The simplified schematic on the first page of the datasheet shows how the two devices work together. The BQ769x0 AFE measures individual cell voltages, current through a sense resistor, and temperature and reports this information to the BQ78350 or a microcontroller.

    The BQ34Z100 is a stand-alone battery gauge. It does not need a companion AFE - it monitors the battery stack voltage and connects to a sense resistor to measure current. The datasheet figure shows it working with a battery protector device, but this specific device is not required - any battery protector can be used. Another similar device to the BQ34Z100 is the BQ34110 - it uses a different gauging algorithm and has a slightly different feature set. The BQ34Z100-G1 tends to be the more popular of the two since it uses the more advanced gauging algorithm.

    I hope this helps. This video may also be helpful: https://www.youtube.com/watch?v=hIBP6UlAyfo

    Best regards,

    Matt 

  • 0
    TI__Genius 10830 points

    hi Jeffrey,
    BQ34z100-G1 is a top of the stack gauge (meaning it will measure the voltage & current going thru your entire battery pack and calculates & reports the SOC) and only a gauge (aka no protection).

    BQ78350-R1 has been defined to work closely with BQ76920: it will take the data measured by the BQ76920 (cell by cell) to calculate SOC using the CEDV algorithm  to provide capacity and health indication but it will also handle:

    • Software protections such as over-temperature, under-temperature, additional levels of over/under-voltage, FET fault, cell disconnection from board, cell severe imbalance

    • Implements cell conditioning algorithm that optimally selects which cell(s) to balance and duration

    • Routinely stores highest/lowest and most significant battery parameters in nonvolatile flash memory for offline diagnostics or forensics (examples: # of charging cycles, min/max temperature, min/max voltages per cell, max charge and discharge current)

    • 3-5 push–button LED or LCD display 

    • SHA–1 authentication

  • 0 in reply to Matt Sunna
    Expert 2875 points

    Must have forgotten to reply...SO, that would mean that 8.2 Functional Block Diagram is incorrect?

    Thanks

  • 0 in reply to Jeffrey Wright
    TI__Guru* 81034 points

    Wow, I'm surprised nobody noticed that before. The functional block diagram is incorrect. There are no SRP/SRN pins on the BQ78350 - these pins are on the BQ769x0 device.

    Thanks for bringing this to our attention!

    Matt