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BQ24133 batter LV disconnect

Brian Sala
Prodigy 60 points
Other Parts Discussed in Thread: BQ24133

Hi,

I intend to use a 3 cell Li-Ion with the BQ24133. When the BQ device switches to battery after the input fails (mains fail), is it correct that the BQ device will shut down when the battery voltage has reached an LV cutoff point? Datasheet section 9.3.6 says the device will shut down when AVCC < UVLO, but Vuvlo is defined as 3.6 volts, so clearly, a voltage divider is needed to set the cutoff voltage for a discharged battery, if this in fact what happens. This area of the datasheet is somewhat confusing, and doe snot fully define the state of the device when in SLEEP, which appears to continue drive to the BATDRV pin.

Can you please indicate if there is a low battery shutdown for this device? ie the battery is disconnected from the load when the mains has failed, AND the battery is discharged.

Else we will monitor the battery voltage with the system processor and shut the device down using the Iset pin. Does that sound OK? ie will pulling Iset low disconnect the drive to BATDRV, or simply disable the charger?

And finally, since the charger uses N-channel FETs, and therefore requires a bootstrap capacitor connected to BTST, that implies a maximum duty cycle for the converter. Can you please indicate the maximum duty cycle of the charger?

Regards

Brian

  • 0
    Prodigy 60 points

    Hi all,

    Thinking about the low battery cutoff some more, it is obvious that the BQ device cannot disconnect a discharged battery due to the body diode of the BATDRV FET (labelled Q3 on the typical schematic), so that question is resolved.

    Still it now is an interesting exercise to find a means to start a system up, and yet have it shut down if the battery runs to its cutoff level- and then restart later!

    Brian