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BQ78350-R1A: cell balancing

Matteo Rigamonti
Expert 1170 points
Part Number: BQ78350-R1A
Other Parts Discussed in Thread: BQ78350, BQ76952, BQ76942, BQ76200, BQ34Z100, BQ76930, BQ34Z100-G1, BQ76940, TIDA-010030

Good morning,

I already used the BQ78350 for several designs and, once again, I'm facing with the same needs. When the application uses an high current for charging the battery pack, the (passive) balancing circuit is not effective in properly balancing cells, especially for old cells, i.e. when their characteristics degraded and differences arises.

The situation could improve a lot if the balancing management could work also during the rest condition and not only during charging. I already asked about this feature and some TI people answered to point it out as a suggestion for future improvements. Unfortunately in last two revisions (R1A and R2) such a suggestion has not been taken into account. I've found other posts with the same request and, to be honest, I don't see any important reason for not implementing such a feature. It could be interesting to add a configuration flag for enabling "balancing at rest" or not, so any user (designer) can carefully evaluate tu use or don't it.

In the user manual I've found a not clear flag related to balancing and rest. It is the flag "SAFE_EN" in the Manufacturing Status Configuration register. In fact the few words related to such a flag are: "Voltage imbalance At Rest". What does it mean? What is the purpose of such a flag? Is that related (or usable) for my need?

I hope my suggestion (but I repeat the same request comes also from other users) will be considered soon for a new release of BQ78350, in order to extend the application field of such a component.

Thank you very much for any consideration and answer

Best regards

Matteo

  • 0
    TI__Guru* 80963 points

    Hi Matteo,

    I agree these would be good improvements for the BQ78350 firmware. The BQ78350 balancing algorithm is limited in scope and only performs cell balancing during charge. Unfortunately, there are no future firmware versions planned for the BQ78350 at the moment. The latest releases of the R1A and R2 firmware last year were a minor change to improve the robustness of the Shutdown routine, so there was no change to the features or functionality.

    The Voltage Imbalance at Rest feature is not for cell balancing. It can be used to permanently disable a pack where the cell voltages have become very different at rest.

    I do suggest you take a look at our new generation of battery monitors that do have the flexible balancing features you mention. The BQ76952 and BQ76942 have the most flexible cell balancing which can operate autonomously or can be fully controlled by the host. There is a new series of videos for these devices and video #4 discusses the cell balancing feature. I also have an app note for cell balancing for these devices that will be published in the coming weeks. 

    https://training.ti.com/training-series-bq76952-bq76942-3-16s-3-10s-battery-monitors

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Expert 1170 points

    Hi Matt,

    thank you for your answer and for your suggestion. Components BQ76952 and BQ76942 are really very interesting and for sure I will test them.

    Unfortunately such new components cannot fully replace the entire chipset made by BQ78350, BQ76930 and BQ76200 because the gas gauging feature is missing. Is there any plan to launch also a companion chip for BQ76952/42 like Bq78350 is for BQ769x0? as an alternative, do you think is it possible to combine the BQ769x2 and BQ34Z100 in the same circuit (i.e. with shunt resistor and I2C bus in common)?

    Thanks again and best regards

    Matteo

  • 0 in reply to Matteo Rigamonti
    TI__Guru* 80963 points

    Hi Matteo,

    There is no plan yet for a companion gauge for the BQ76952/42, although it is possible we will develop one in the future. The BQ34Z100-G1 is a good option to use with the BQ76952/42 because it is a stand-alone gauge and can share the shunt resistor.  There is a TI design that might be helpful using the BQ34Z100-G1 with the BQ76940 battery monitor - TIDA-010030.

    Best regards,

    Matt