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BQ77904: Reverse charge protection of each cell in a 3S configuration

user5252159
Intellectual 260 points
Part Number: BQ77904

Hi,

See the schematic below. Will this circuit protect the individual cells from reverse charge if one or more of the cells are inserted in wrong direction? Or do I need to add extra protection across each cell, e.g. diodes in parallel with each cell?

PS: don't look at the resistor values in the schematic as these aren't defined yet.

  • 0
    TI__Guru 54715 points

    Hi User,

    The BQ77904 does not protect for reversed cells.  If BT1C was installed backward it would try to drive a negative voltage on VC1 violating the abs max of the part and allowing discharge of the cell. Reversing BT1B or BT1A only should not provide a negative voltage on an input, but with 2 cells providing a positive voltage and 1 a negative voltage the part could have a voltage above V(POR) causing the part to allow charge of the cells.  The one cell would be under voltage but would not prevent charge.

  • 0 in reply to WM5295
    Intellectual 260 points

    Hi,

    Thank you for your answer. Have you seen solutions for protecting against reversed cells that could work in my application? Suggestions are appreciated.

  • 0 in reply to user5252159
    TI__Guru 54715 points

    Hi User,

    I have not seen electrical solutions for reversed cells with the BQ77904.  The device is commonly used for permanent assemblies where the cells are not removable.  I have seen mechanical mechanisms for other cell types to prevent connection if reversed, I don't know if those might be available for your application.