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BQ25792: POR definition and some questions

Roy Chou1
Genius 16055 points
Part Number: BQ25792
Other Parts Discussed in Thread: BQ25798

Tool/software:

Hi Team,

1. I want to know the POR definition of the BQ25792. If battery is connected, but re-plug in VBUS, does this action mean POR?

2. Currently, we have Vbus and battery connecting the BQ25792. Now we re-plug in the Vbus and we don't want the 1h/3h/5h/6h the register setting changed. Do we have any bit can achieve the function?

3. For the CC/CV threshold, it's regulation voltage that we set, but I'm not sure if we can set VREG_low threshold which means that if the battery discharge the voltage and its value low than VREG_low threshold and then enter in CC mode to charge, but the VREG_low threshold isn't the same as VREG.

Regards,

Roy

  • 0
    TI__Guru**** 165886 points

    Hi Roy,

    Regarding 1, POR is when both BAT and VBUS voltages fall below their respective UVLO thresholds and then either one or both have a voltage applied above their UVLO thresholds.

    Regarding 2, the charger has a watchdog timer that resets several registers including safety timer if the WD bit does not receive an I2C write before the timer expires.  This is likely what is resetting your timer because VBUS remove/replace with battery present does not do that.

    Regarding 3, VBAT_LOWV is the transition point between pre-charge and fast-charge.  You can change the threshold as a % of VREG in REG0x08[7:6].

    Regards,

    Jeff

  • 0 in reply to Jeff F
    TI__Genius 16055 points

    Hi Jeff,

    Thanks for comments.

    1. Regarding #3, if our battery is charging by BQ25792 and fully be charged. Not sure if we can stop the BQ25792 charging the battery  and if battery voltage under VBAT_LOW, return to charge the battery. This is the real time flow. 

    2. For the initial operation of BQ25792, i think it would check the battery voltage value and operate in corresponding mode, is it correct?

    For example, if battery voltage within VBAT_LOW and VREG, it would enter in CC mode. 

    For example, if battery voltage over VREG, it would enter in CV mode.

    Regards,

    Roy

  • 0 in reply to Roy Chou1
    TI__Guru**** 165886 points

    Hi Roy,

    1. charge restarts when the battery voltage at BATP pin drops to VREG-VRCH (set in REG0x0A).

    2. correct.

    If your battery is user removable/replaceable, I recommend moving to BQ25798 to prevent 30ms converter shutdown (and likely SYS collapse) at battery removal while charge is enabled.  798 is pin2pin and reg2reg compatible with 792.

    Regards,

    Jeff