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BQ24123 Safety Testing

ROBB MAIN
Prodigy 20 points
Other Parts Discussed in Thread: BQ24123

Currently having a BQ24123 design run through IEC 61010 safety testing. Test lab is suggesting shorting Pin 3 (input) to Pin 10 (output) as a valid failure to test. This would simulate the internal FET failing SHORTED. First off, does this happen, verses failing OPEN?

Secondly, assuming the FET can fail shorted, would the BQ24123 over-current trip?

Third, if the over-current did trip, would it be able to SHUT DOWN, if the FET was failed shorted? I think not.

Is there some other additional protection that might be commonly added to protect against this kind of eventuality (such as a PTC in series with the battery)?

If there was no way to shut down the current in this failure mode, the battery pack contains internal protection, which should trip, provided the charging current exceeded it's maximum rating.

Thanks,

Robb.

  • 0
    Expert 2225 points

    Hi Robb,

    I am not aware of operating details of the BQ24123 but I have a fairly generic solution.


    As an additional level of safety, you may consider adding a fuse.  However, a discharged pack may not have sufficient energy left in the tank to blow the fuse. 

    Here comes in the SCP from Dexerials.  That is basically a fuse that has a blow port.  You can force it to blow in case the other protections have failed.

    As for the PTC, be aware that many cells have one builtin.  Ask your manufacturer about it. Here again, it may not kick in if your pack is weak or that the load is just not heavy enough.

    Hope it helps.

    Fred

  • 0 in reply to Fred P
    Prodigy 20 points

    Thanks for the tip, Fred.

    I was not aware of the SCP. Using a second circuit as a heater for force a fuse to blow seems an eloquent solution, though it does require some kind of supervisory function (either in the charger directly, or the platform MCU (which would also require some way to monitor current)).

    I'm not sure the SCP will integrate well in this design, but it will certainly be added to my "bag of tricks" for future work.

    Cheers,

    Robb.