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BQ25890H: Reverse battery protection

Jitender Misra
Prodigy 150 points
Part Number: BQ25890H
Other Parts Discussed in Thread: BQ27742-G1

Hello, 

we have a design with BQ25890H, we are using the same to charge two 18650 cells connected in parallel. My question is that whether BQ25890H has inbuilt reverse battery protection ? If No , what will be the impact of connecting battery in reverse polarity to BQ25890H BAT_RAIL pins?

Regards

Jitender

  • 0
    TI__Guru**** 166626 points

    Jitender,

    None of our chargers have reverse polarity battery protection.  Either the battery or charger could be damaged by reverse polarity battery.  You can add protection using a FET with body diode as explained here:  www.ti.com/.../slva139.pdf

  • 0 in reply to Jeff F
    Prodigy 150 points

    Hello Jeff, 

    Incidentally forgot to mention that we do not connect the charger directly to batter, in fact the BAT_RAIL output from charger passes through charging and disharging FET's ( TWo NMOS ) connected in series with each other before getting connected to battery Pack rails.. These FET's are in turn controlled by TIgauge IC BQ27742-G1. See the FET's Q5 and Q26 in the below circuit , which come in series with the Node BAT_RAIL which is supplied by the BQ25890H charger. IN view of below circuit , can you comment whether the charger will be protected from reverse battery connection because of the below circuit. 

    Regards

    Jitender

  • 0 in reply to Jitender Misra
    TI__Guru**** 166626 points
    Jitender,

    Unfortunately, no. You will still need to add some other method for reverse battery polarity protection.
  • 0 in reply to Jeff F
    Prodigy 150 points

    Hello Jeff,

    can you please explain a little more , my understanding is that once i  protect the gauge alone against reverse protection , the gauge will not get power in case of reverse voltage connection, so it is not going to drive the Q7 and Q26 FET's Also a negative voltage on Q7 source pin will not get anyway path through Q7. So if that is the case , How will the reverse voltage affect my circuit. can you please explain  a little more ?

    Regards

    Jitender