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BQ2970: reverse polarity protection for 2x 18650 LiPo batteries in parallel

Gabriele Rizzi
Prodigy 100 points
Part Number: BQ2970
Other Parts Discussed in Thread: BQ25895, BQ2980

In my application, I have to use 2x 18650 batteries in parallel for capacity reasons. At the same time, for marketing reasons, I need to use removable 18650 elements, using a battery holder on board, and so the chance that batteries might be inserted backwards is definitely not negligible.

I was thinking of protecting each battery with a BQ2970, adding an extra mosfet to keep the charge mosfet off, as mentioned in a few posts, and then connect the output of the two protection circuits in parallel.

Would this work? or would you recommend a better/alternative solution?

FYI the charger is implemented using a BQ25895 on the main board - and hence can never be connected wrongly.

Looking forward to reading from you.

Gabriele

  • 0
    TI__Expert 7035 points

    Gabriele,

    For this application, I would suggest you use the BQ2980. It is a similar device to the BQ2970, however it has high-side primary battery cell protection instead of the low-side in the BQ2970. Here is the data sheet:

    http://www.ti.com/lit/ds/symlink/bq2980.pdf

    The device itself does not protect against reverse current, but you can make some simple additions to the board for this protection. You need to add a small signal NFET whose gate is is connected to ground, the source and drain across the gate, and source of the charge FET to short them together in the event of a reverse charger connection. In the event of a reverse current, the FET will turn off and protect the batteries. We have a schematic of this configuration for a similar device for reference. See Q2 in Figure 21 on this document:

    http://www.ti.com/lit/ug/sluubp4/sluubp4.pdf