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BQ76952: Use of several modules, each with one BQ76952 in parallel

Christopher Hackl
Prodigy 20 points
Part Number: BQ76952
Other Parts Discussed in Thread: BQ77216, TIDA-010208

Tool/software:

We are planning to develop a scalable battery system.
This means we want to have a ‘standard’ module with 14S, each with a BQ76952. Each module should have a slave BMS, so to speak.
In order to be able to vary the capacity of the battery, we want to connect between 1 and 4 of these modules in parallel.
The question would now be, is it possible to operate several BQ76952 in a parallel configuration?
If it is possible, what do we need to bear in mind?

I also have a question about your reference design TIDA-010208: Why is a BQ77216 also used here? The BQ76952 would also be able to trigger a fuse. In other words, when is it necessary to use a BQ77216 and when could it be omitted?

  • 0
    TI__Genius 17945 points

    Hello Christopher,

    I believe these two documents might also be useful as reference to help with your design.
    1. Design Considerations of Stacked BQ769x2 With High-Side N-MOSFET
    2. How to Stack Battery Monitors for High-cell-count Industrial Applications

    From what I can see for the TIDA-010208 reference design, I believe the BQ77216 is being used as a secondary protection. You are correct that the BQ76952 could trigger a fuse as well if that is your design choice.

    In Section 1 System Description of the reference design, it mentions that this secondary protection is ‘an add-on board and can be easily removed and added based on actual demands’, so you may choose to remove it if you do not want the additional features a secondary protector IC could provide.

    The 'need' of it depends on system requirements and the user is concerned about. In Section 2.1 Block Diagram, it mentions that the design uses the BQ77216 for voltage and temperature protection to help ‘the design pass some safety regulations without requiring an MCU to carry out protection work’. 

    Best Regards,
    Alexis

  • 0 in reply to Alexis_H
    Prodigy 20 points

    Hello Alexis,

    I already knew the two linked documents, but I haven't looked at them in detail yet because I was always looking for documentation for parallel connection. However, there are some important points to take away from the documents.
    For me, the two most important ones are

    • Communication --> Changing the I2C address
    • Drive Mosfets --> Linking the control signals for the mosfets. What would be the best solution for this?

    Because of the secondary protection, we probably just have to analyse whether a BQ77216 is needed, for example, according to the required performance level.

    Thank you very much for your support.

    Kind regards
    Christopher 

  • 0 in reply to Christopher Hackl
    TI__Genius 17945 points

    Hello Christopher,

    Thank you for your patience. After checking with my team as well, we unfortunately do not have any specific material to offer regarding connecting our parts in parallel other than parallel paths for the charging and discharge FETs in one module (Parallel Paths with the BQ769x2 Battery Monitor).

    However, I think this previous post may be somewhat helpful: BQ76952 Parallel Connections

    Best Regards,
    Alexis

  • 0 in reply to Alexis_H
    Prodigy 20 points

    Hello Alexis,

    The link to the post also helped me a bit, but I still need a clear statement as to whether it is possible to connect several BQ76952s in parallel or not.

    Our system would look like this

    • In production, 1, 2, 3 or 4 modules are combined with one BQ76952 each to create a battery. It is ensured that each module has the same state of charge.
    • The first BQ76952 controls the mosfets and measures the current
    • Each BQ76952 measures the temperature and voltages of its module and has its own I2C address

    Is it possible to link the DSG and CHG signals of the individual BQ76952s (AND link) so that the mosfets only conduct when all ICs give their OK?

    Is the request to connect several BQ76952s in parallel so unusual that there is not really an answer yet?


    Kind regards
    Christopher

  • +1 in reply to Christopher Hackl
    TI__Genius 17945 points

    Hello Christopher,

    It is possible to connect several BQ76952s in parallel. This previous post (Link) may also provide some extra things to consider. It should be possible to link the DSG and CHG signals of the individual AFEs so that the MOSFETs only conduct when all ICs give their okay. There is an answer of if it is possible, but the specifics/details of how to best achieve it has not really been experimented with.

    Best Regards,
    Alexis

  • 0 in reply to Alexis_H
    Prodigy 20 points

    Hello Alexis,

    Thank you for your reply.
    To summarise, it should be possible to use the BQ76952 in parallel and there is basically nothing to be said against it. However, there is little to no experience of this in practice.
    We will probably just have to try it out and make our own experiences.

    Kind regards
    Christopher