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BQ24295 - Setting a power cutoff level

Brian Antheunisse
Expert 5305 points
Other Parts Discussed in Thread: BQ24295

Hi Team,

I have a customer who is experiencing a issue on a board and are trying to figure out a way to prevent it.

 

"Our circuit uses a BQ24295 which can be charged from a USB connection. In addition to the

BQ24295 we have a BQ27621 guage on the battery side. We create

1.8V for our controller that comes from a TPS62231DRY that is fed with the battery voltage.

 

The issue we have is as the battery depletes below normal operating range. We have no mechanism

To cutoff the battery except the battery protection circuit which is set for 2.5 to 2.7v. As a result our

Circuit is attempting to restart (includes a speaker) but is not successful due to the battery being too depleted. Is there a

way to get the BQ24295 to cutoff power around 3.1V and then turn back on once charging resumes?

Any other ideas?"

Thanks,

Brian

  • 0
    TI__Expert 8230 points

    Hello Brian,

    If the 1.8V step-down is connected directly to the battery (BAT pin of the charger) they would need additional circuitry to cut-off the power completely, besides using the protection ICs.

    If the 1.8V step-down is connected to the SYS pin of the bq24295, there are couple scenarios to explore:

    • If host is operating from battery, the internal BATFET of the bq24295 will be on providing a discharge path out the SYS pin to power the 1.8V step-down. The BATFET will remain on until the Battery voltage reaches the battery depletion threshold, VBAT_DPL, typically 2.4V. After this, it turns off and waits until the adapter is plugged in to charge the battery and power the system.
    • If they want to cutoff the power to the system when the battery is around 3.1V they could configure the gauge's SOC1 and SOCF thresholds to a capacity value needed to perform an orderly shutdown protocol or just use the voltage measurements to determine when VBAT = 3.1V. After this, the host can force the internal BATFET off by setting the I2C bit REG07[5]. Note that at this point the host and any peripheral will lose power (since forcing the BATFET off prevents discharge and charge of the battery).
    • At this point the user needs to plug in the adapter to charge the battery. Once the adapter is plugged in, the SYS pin will regulate to the MINSYS threshold and provide power to the 1.8V step-down. The host then can run the initialization routine and ensure REG07[5] is cleared and charging is enabled.

    Hope this helps.