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BQ24450 reverse Battery protection

Bornfree
Prodigy 240 points
Other Parts Discussed in Thread: BQ24450

Hi there,

 

I just want to know of the BQ24450 pins 7,10,11,12 and 13 have any sort of reverse battery protection? Since these pins are before the blocking diode. What effect will it have it these are connected after the blocking diode? In case someone connected the battery the wrong way around! I have a LED indicating reverse battery, but is there any protection on the chip?

 

Cheers

  • 0
    TI__Guru**** 150950 points

    Because the abolute maximum rating on each of the referenced pins only goes down to -0.3V, the pins will not withstand a reverse connection.  In that case, each pin would be below ground by the battery's voltage.

    Pin 11, pre-chg, can handle up to -32V so it is ok.

    The best solution is to mechanically key a connector that goes from the charger to the pack.  This is a fail safe way of preventing a reverse connection.

  • 0 in reply to Chris Glaser
    Prodigy 240 points

    Chris,

     

    Thank you very much for your help. But i'm working on a charger as a stand alone where customers will connect their own battery. Chances are they will connect wrong battery polarity into the terminal blocks.  Would you recommend using a schottky diode before the resistor divider network and removing the Dext or will this compromise my battery charging values?

  • 0 in reply to Bornfree
    TI__Guru**** 150950 points

    Yes, you can use a P-channel FET between the battery pack and the board.  Connect the gate to the battery's negative lead.  Connect the drain to the battery and source to the charger.  In this configuration, the body diode will not allow current to flow when a battery is put in backwards.

    Adding anything after the resistors that sense the battery voltage and the battery will alter your charge voltages due to the IR drop.  With a low enough Rds-on FET, this shouldn't affect it much.