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BQ76200: Power management forum

Riccardo Consolo
Prodigy 20 points
Part Number: BQ76200

Good morning, I have a question about the BQ76200 driver. I'm using it for a two wire system to control the charging and discharging of a battery. I separeted the two charging and discharging paths, placing two power mosfets connected in antiseries in both branches, like in the image, to simplify the view i don't put all the mosfets, only the two of the charge path and of the discharge path, in total i have more mosfet connected in parallel to suport the current for my application.

The problem I encounter is that when I set CHG_EN to 0V, the voltage on the CHG pin, is not 0V but VBATT, CHG moves between VBATT and VBATT+10V, which it it would be the voltage of he chrarge pump. I don't understand why is not 0V.

  • 0
    TI__Mastermind 42060 points

    Hello Riccardo,

    Correct, CHG will turn-off by driving its voltage to VBATT, the high-side MOSFET for the CHG FET has its source typically connected to the BATT+ of the device, so the voltage across the gate-source of the FET is approximately 0-V when the CHG FET is OFF.

    You can see explanations of this in Section 5 CHG Circuit and of the bq76200 Beyond the Simple Application Schematic application note.

    This is the way that the FET driver was designed. 

    For the DSG FET, its source should be in reference to the PACK pin. This is its source-reference. So you should have DSG FETs in common-source configuration and have the PACK pin connected between the FETs.

    Are you separating the charging/discharge path due to the different current requirements?

    If charging current is small enough, you could use a blocking diode instead of the MOSFET. Or you could do more complicated circuits to block discharge currents through the charge path.

    Have you also considered using other FET drivers that may be able to switch both directions of currents by default?

    Best Regards