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use BQ76940EVM with actual batteries.

Ran Aloni
Expert 2386 points
Other Parts Discussed in Thread: BQ76940EVM

Dear all,

we would like to test the BQ76940EVM with actual batteries,
I couldn't find in the user guide explanation on what needs to be done.

I removed resistors R129-R138.
anything else? should I remove R122 too?

many thanks,

Ran

  • 0
    TI__Guru 54715 points
    Generally a user would simply open all switch segments on S3 and S4, then connect the cells first BATT- (J1), J5, J9 and finally BATT+ (J2), or connect the cells then open the switches. See section 6.5 in the user guide although it uses a general description.
    If S3 and S4 are not opened the cell simulator will discharge the battery.
    If some resistors have been removed as you describe, do not operate with a power supply attached and the simulator switches closed since any remaining cell simulator resistors will create a large differential voltage on the inputs.
    If you have removed all the cell simulator resistors, opening S3 sections 1 and 2 should prevent operation and discharge of the cells into the LED.
  • 0 in reply to WM5295
    Expert 2386 points

    thanks Willy,


    so leave S3,S4 will solve it.
    about order of connection.
    in my actual schematics, I cannot physically guaranty the order of cell connection.

    B- and B+ will be connected first, not sure what order, and then, V0-V6, followed by V7-V12 and V13-V14 (it is a 14S configuration).

    what should I expect?

    should I find a solution for this?

    regards, Ran

  • 0 in reply to Ran Aloni
    TI__Guru 54715 points

    Generally it should work fine, the part is designed for random cell connection.  However 14 cells will provide a lot of voltage which could distributed across the inputs by the application circuitry or assembly tooling in a way to exceed the abs max ratings of the part. The chance of overstress may be less if the connectors match the groups on the IC (for 14 cells it might be V0-V5, V6-V10 and V11-V14).  You might look at www.ti.com/lit/slua749, section 10.  Connecting V6 might normally be a concern, but if you have already connected B- and B+ the power supply capacitors will already be charged.  You may need to limit some voltages in a manner specific to your circuit construction and assembly process.

  • 0 in reply to WM5295
    Expert 2386 points

    Dear Willy,


    PCB is built (because of mechanical reasons) to accept:

    randomly main B- and B+.

    then harness with V0-V6 , V7-V12, V13-V14.

    1) is connecting main B+ before B- a problem? should I make sure they are separated from V0 and V14 first?

    2) from your explanation we expect no issue once B+ and B- are connected and then we connect the harnesses one by one.
    because V6 is connected well after capacitors are full.

    thanks, Ran

  • 0 in reply to Ran Aloni
    TI__Guru 54715 points
    1. Connecting B+ or B- first should be fine, the board does not know there is a difference unless there is some other connection through the fixture. Separating V14 from B+ may be desirable particularly if P-ch external balance FETs are used. V0 should be fine since it is referenced to B-.
    2. Correct, the voltages are expected to be close to the final value and there should normally be only a minor adjustment in voltages when the harnesses are connected. Each system design should be evaluated of course. Leakage paths in the fixture or inadventent connecitons in assembly fixtures could cause excess voltages, or if the harnesses could inadvertently touch the wrong contact during handling.