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BQ40Z50 vs. BQ4050

Ara Adamian52
Prodigy 40 points
Other Parts Discussed in Thread: BQ40Z50

I am trying to pick a fuel gauging algorithm for my application, and have gone through the presentation "D1 - Track 1 - 2 Gauging Algorithm Comparisons - CEDV, Z-track various generations, PL114, DVC.pdf", but still have questions.

It seems like impedance tracking is the preferred fuel gauging algorithm in most categories (slide 36), but I don't really understand categories like "State of Charge initialization (host side requirement)" and the voltage accuracy requirement.

In my application, the battery management IC will live in the battery pack that is expected to have ~100 cycles.  If I am looking to have the highest accuracy fuel gauge, should I get the impedance track version (BQ40Z50 )?

Thanks!

  • 0
    TI__Mastermind 27145 points
    Hi Ara,

    State of Charge Initialization is for host side gauges in which the battery is removable. These gauges take an OCV reading when a battery is inserted to determine the state of charge of the battery.

    The voltage accuracy requirement refers to the necessary accuracy for OCV readings when the battery is at rest

    Impedance Track gauges are typically more accurate over the life of the battery. If accuracy is a high priority for you, I would recommend using the BQ40Z50

    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    Prodigy 40 points

    Thanks Ben. Can you also confirm that it doesn't matter if the Pack+ pin and SMBus pins connect to the host system before the ground pin on the pack does? It doesn't look like the return path will go through the SMBus pins and cause harm to the IC/SMBus (because of the high series resistance), but I wanted to be sure.

    Thanks again!

  • 0 in reply to Ara Adamian52
    TI__Mastermind 27145 points
    Hi Ara,

    Just for clarity, is this question regarding the application schematic shown in the bq40z50 datasheet? If your CHG and DSG fets are on when this occurs, you will want to be careful with the amplitude and duration of the current spike.

    I don't foresee issues with the SMBus pins but be careful not to exceed the rated voltage for the coulomb counter which could happen if there is large current flowing through the sense resistor.

    Best Regards,
    Ben Lough
  • 0 in reply to Benjamin Lough
    Prodigy 40 points
    Ben,

    Yes, we are using the application schematic and integrating this circuit into a battery pack. My question is, when the battery pack makes contact with the host system, do I have to worry about the ground contact making connection before the SMBus pins. In other words, is it possible for the host system to damage the SMBus by Pack+ and the smbus pins being connected before the ground contact (because the host system is trying to get its return through it)?

    Thanks!
  • 0 in reply to Ara Adamian52
    Prodigy 40 points

    Ben,

    One more question: Is the second over voltage protection IC (BQ296103DSGR in the application schematic) really necessary if I don't use the inline chemical fuse? These seem difficult to source and I cant find a distributor to buy any from.

    Thanks,

    Ara

  • 0 in reply to Ara Adamian52
    TI__Mastermind 27145 points
    Hi Ara,

    If you include the zener diodes and series resistors on the SMBus lines, I do not foresee issues with the SMBus in the scenario you described.

    You can rely on the protections built in the bq40z50 if you choose not to include a fuse. It really depends on your application and what level of protection you are confortable with.

    Best Regards,
    Ben Lough