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BQ25703A: How to manually enable the prechrge mode

Zhaohong Zhang1
Intellectual 300 points
Part Number: BQ25703A
Other Parts Discussed in Thread: BQ40Z50-R1, BQ40Z50,

The 3 cell battery we use has an internal gas gauge based on TI bq40z50-R1. When battery is in undervoltage condition, bq40z50 disables discharge and the voltage at the battery terminal is zero. We found that we can revive the battery by taking the battery out of the system and directly applying 12V to it.

The question is how to revive the battery without taking it out of the system. Our charging circuit is based on TI bq25703A. Is there a way to force precharge mode when the battery voltage is zero?

There is a SMBUS at the battery connector. Is there a way to communicate with the bq40z50 to enable discharge so that the voltage at battery terminal is not zero? From the bq25703A data sheet, it seems that bq25703A can automatically enter precharge mode when the battery voltage is below a threshold.

Thanks,

Zhaohong

  • 0
    TI__Mastermind 25800 points

    Hey Zhaohong,

    By default, the BQ25703A has an AUTO_WAKEUP_EN bit which is meant to do this very thing. Autowakeup is used for gauging + protection devices that disable the discharge FETs whenever the battery is depleted. The AUTO_WAKEUP_EN bit applies a 128mA charging current into the battery node to re-awaken the protection circuitry for charging.

    This bit is enabled by default.

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Intellectual 300 points

    Joel,

    Thanks for the reply. The issue we have is that the voltage at battery terminal is zero when undervoltage condition occurs. In this case, would bq25703A consider that the battery is removed? We connected such a battery to bq25703A and observed zero volts at the battery terminal. Do we need to force the gas gauge inside the battery package to enable the discharging FET so that bq25703A can see some voltage?

    Thanks,

    Zhaohong

  • 0 in reply to Zhaohong Zhang1
    TI__Mastermind 25800 points

    Hey Zhaohong,

    In this case, we will not recognize the battery as removed. The charger is looking purely at the voltage at the SRN pin (our BAT pin voltage sensing) and the AUTO_WAKEUP_EN will force 128mA into the node. 

    When you connected the battery to the BQ25703A, did you use an EVM? Did you have an input source connected to VBUS?

    Regards,

    Joel H