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What is best choice for secondary protection of 3s configuaration: bq2945xx or bq2947xy when using bq40z60?

Mark Arsenault
Intellectual 420 points
Other Parts Discussed in Thread: BQ40Z60

We are designing a LiIon battery pack that most likely will be based on the bq40z60.  For secondary protection the SLUSAW3C Figure 8 Typical Application Schematic shows a bq294700.  This example is for 4 series cells.  The associated Note indicates to use bq2945xy for 3s configuaration.  The bq2947xy datasheet indicates this part also works for 3 series cell configurations.  This part has a external delay capacitor -  under what conditions is this external delay required?

  • 0
    TI__Genius 10785 points
    Mark,

    You want to have delay in all condition. You don't want some noise or transient to turn on the FET and blow the fuse. I suggest you to have delay in your system.
  • 0 in reply to Roger Hwang
    TI__Genius 10785 points
    Mark,

    BQ2945XX is 2-3S OV with fixed delay time.
    Bq2947xy is 2-4S OV with external delay.
    Bq2960XY is 2-4S OV with few delay options with LDOs.

    What do you looking for then I can give you better answer ?
    It seems like all of three ICs will work for you.

    You only need 1 protector for 3S3P config.

    Roger
  • 0 in reply to Roger Hwang
    Intellectual 420 points
    Our belief, at this point that we need 3 protectors because this application must meet ATEX Directive (protect employees from explosion risk in areas with an explosive atmosphere) requirements, we must measure to guarantee that none of the cells exceeds its charge/discharge specs. This includes parallel cells, even though we believe that should reach equilibrium naturally. Looking for a better approach that will guarantee we meet the directive. Also, how to determine if internal delay is adequate or if external delay is required during the design phase?
  • 0 in reply to Mark Arsenault
    TI__Genius 10785 points
    Check the delay time you need and select the device.
    You can have fixed delay time or use external cap to set the delay.