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BQ77905: CHG and DSG mosfet on positive line (disconnection)

Blaz Jakob1
Prodigy 10 points
Part Number: BQ77905
Other Parts Discussed in Thread: BQ76200

HI,

so I have the case, where I have 4 LiPo battery cells and I need common ground  between charger and battery balancer BQ77905.

Have anyone try to put mosfets on the positive line, for disconnecting charging and discharging. Will this work the same way?

Regards

  • 0
    TI__Guru 54715 points

    Hi Blaz,

    You can use high side switching FETs, but there are complications.  A high side P-channel charge implementation is shown in http://www.ti.com/lit/pdf/slua910 .  As described in the application note, one of the design choices with a P-channel switch is how much current to use to bias it, and another is how to turn it off quickly.  A P-channel discharge FET can be implemented similarly, fast turn off may be more of a concern for the discharge FET.

    Another choice may be high side N-channel FETs, these will need some driver.  The BQ76200 can provide the level shift and high side FET drive, it does require current.

    With a high side switching you will need to determine how to control the LD pin if required.  If you have a MCU available it can switch the pin, otherwise you may need some comparator circuit or pull up and transistor to pull LD low when appropriate for recovery.