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BQ25792: Way to place BAT pin in high impedance mode?

Peyton
Prodigy 50 points
Part Number: BQ25792

Hello,

We want to discharge the battery as it is plugged into the charging board, but I am concerned the BQ chip could sink current and become damaged since the BATFET body diode would allow current to flow to SYS. Our discharge current is not high, maxing out at 160mA. Do we need to modify the design to use the OTG function and have the second input source be the discharge circuitry, or is there a way to put the BAT pin of the BQ25792 into a high impedance state and prevent current flowing through the IC? I do not see way to set the charger to output 0mA in the data sheet ( the lowest output current seems to be 40mA). I believe setting the BQ chip to the lowest current setting would work but am not sure if that is advisable for the health of the IC. 

Thanks,
Peyton

  • +1
    TI__Guru**** 150335 points

    HI Peyton,

    The BATFET cannot be turned off due to the body diode.  The only way to isolate the battery from SYS is to use an external shipFET, controlled by SDRV pin.  Then the host force the charger into ship mode or shudown mode.  The BATP pin sinks a small amount current even in ship mode. 

    With no input power attached, the charger auto enters high Z mode so no issue with discharge then.  If input power is attached, the host can set EN_HIZ bit = 1, which turns off the converter and then you could discharge the BAT and BATP pins.  Also, there is 30mA pull down on BAT that the host can turn on using REG0x0F[6].

    Regards,

    Jeff