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multi-cell fuel gauge

Bob White
Intellectual 660 points
Other Parts Discussed in Thread: BQ78PL114, BQ78PL116, BQ76PL102, BQ34Z100

I am making a Battery Management System for a 7 to optional 10 cell LiPo battery, now 7S4P.  75 Amp max output.  I'm a bit scared by seeing the post "BQ78PL114 + BQ76PL102 fail randomly" on this site, but the BQ78PL116 looks like my only choice, hoping that the '116 upgrade was the solution to said problem.  My main requirement is Fuel Gauge, I don't plan on using the power-pump balancing - we use a balancing charger.

I have these questions:

1.  Is the '116 a reliable product?

2.  Is it OK to not use the power pump, but still use the '116 for secondary protection and State of Health?

3.  Is the '116 the reccommended part for this application?

4.  Can I get a passive balance (no inductors) out of the '116, for shelf life?

5.  Is there a better multi-cell Fuel Gauge?

Thanks,

Bob

 

  • 0
    TI__Guru 73830 points

    Bob,

    1) The PL116 is a reliable device. The failures that you were referring to are associated with communications between the PL114 or PL116 and the PL102 devices over the PowerLAN interface. We have found that the failures are due to noise getting coupled onto the traces and causing communications problems, so care must be taken when routing these signals.

    2) You can used the device without using the PowerPump feature. The PowerPump can be disabled in the System Control register.

    3) That depends. You are using LiFePO4 devices and we are finding that users want to discharge them to lower cell voltages than the device can support. The measurement systems on the device is not guaranteed to operate below 2.75V, so you will not be able to use the full voltage range of these cell chemistry.

    4) These devices are not configured to support passive cell balancing.

    5) The PL114 and PL116 will be the most integrated solutions that we currently offer to support a 7s pack. We also offer the PL536, which offers passive cell balancing and cell monitoring / protection for 6 channels. It would have to be combined with a gas gauge device for current monitoring and FET control.

    I hope that this helps.

    Regards

    Tom

  • 0 in reply to ThomasCosby
    Intellectual 405 points

    Hi Tom,

    One year after this post, we get the information that PL114, PL116 and PL102 are not recommended for new designs. 

    As you said, these devices suposed to be the most integrated solution for pack management. The recommended bq34z100 is by far not so integrated, that must be combined with others devices.

    Is there possibility in the near future to employ these devices again for new designs?

    Thanks

     

  • 0 in reply to Douglas Malouf
    TI__Guru 73830 points

    Douglas,

    These PL devices will remain in production and you are free to use them, but we will only be able to offer limited support for them. One reason that they were moved to NRND is that they are complicated devices and usually require a lot of applications support to complete a design. The other primary reason is that they do not work well with LiFePO4 cells and a lot of users were moving towards those types of cells. The bq34z100 gauge will support LiFePO4 cells and we are also releasing a new family of CEDV type gauges to support high cell count applications.

    Regards

    Tom