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BQ25792: Are we protected against reverse battery

Kiran Kerai
Prodigy 200 points
Part Number: BQ25792

The BQ25792 is configured to charge 3S battery up to 12.6V. The batteries are replaceable.

Does this device protect itself if batteries are fitted the wrong way round i.e. up to -12.6V on BAT terminal

  • +1
    TI__Guru**** 166106 points

    Hi Kiran,

    No.  The charger has no protection against reverse battery.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 200 points

    To protect against reverse battery we need two nodes (BAT and BATP) to be disconnected from the battery. Please confirm both these are unable to withstand negative voltages in reverse battery mode.

    1) For BATP can a diode be placed to gnd (anode at gnd, cathode at BATP) the upstream 100 ohm resistor will provide current limit and diode will clamp at -0.3V max

    2) For BAT, we have a ship fet fitted and I assume this will open if we drive CE high? Will monitor battery voltage and drive CE low only if battery voltage is positive.

    We have limited space in our design so would appreciate if there is any other way to do this that would save space.

  • 0 in reply to Kiran Kerai
    TI__Guru**** 166106 points

    Hi Kiran,

    Regarding 1, that should work in theory but I haven't tested.

    Regarding 2, ship FET will only close (turn on) if there is a positive voltage on BATP (assuming no voltage on VBUS).  The shipFET does not open unless the ship mode or shutdown mode bits in REG0x11 are written.  

    I predict this will working if there is no voltage on VBUS but I don't know what will happen if there is a voltage at VBUS.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 200 points

    Regarding 2, we may have VBUS voltage battery reversed. Will CE high not open ship fet? Is our only option to disconnect VBUS?

  • 0 in reply to Kiran Kerai
    TI__Guru**** 166106 points

    Hi Kiran,

    CE high does not open the shipFET.  It disables current flow from SYS to BAT through the IC's internal BATFET.

    Regards,

    Jeff