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BQ25895: Will the device reset when Vbus falls below VBUS_UVLOZ and then rises above VBUS_UVLOZ when the battery is 4.2V and connected to VBAT?

Howard Zou
Genius 12365 points
Part Number: BQ25895

Hi, I have two questions for this device:

1. Will the device reset when Vbus falls below VBUS_UVLOZ and then rises above VBUS_UVLOZ when the battery is 4.2V and always connected to VBAT?

2. For relative VINDPM, when VINDPM_OS is 600mV default value, I plug in a 6V adaptor, the VINDPM will be (6-0.6)=5.4V, correct?

If VBAT connected to a 4.2V battery, and I unplug the 6V adaptor and plug in a 5V adaptor, VINDPM will still be 5.4V or it will be updated to (5-0.6)= 4.4V automatically?

  • 0
    TI__Guru**** 166306 points
    Hello Howard,

    Regarding 1, no. If V(BAT) > VBAT_UVLO then the register settings are retained even if VBUS falls below VBUS_UVLO.

    Regarding 2, yes. With relative VINDPM, VINDPM=V(VBUS)unloaded-VINDPM_OS. If VBUS_HIGH falls below VBUS_UVLO during remove/replace with VBUS_LOW then relative VINDPM properly identifies the new VINDPM setting.

    Regards,
    Jeff
  • 0 in reply to Jeff F
    TI__Genius 12365 points

    Jeff,

    so if VBUS falls but is always above VBUS_UVLO, the relative VINDPM will not identify the new VINDPM, right?

  • 0 in reply to Howard Zou
    TI__Guru**** 166306 points
    Howard,

    Correct. If VBUS droop is a concern, then I recommend
    1. periodically measuring the VBUS voltage with the ADC and then
    2. using the FORCE VINDPM bit to change to absolute VINDPM

    Regards,
    Jeff
  • 0 in reply to Jeff F
    TI__Genius 12365 points
    Jeff,
    my customer also find that for HIZ mode.
    It will be reset (REG00[EN_HIZ] go back to 0) when I unplug and then plug the adaptor when battery is attached.
    Since the action will not trigger a reset.
    Is this normal for HIZ register bit change from 1 to 0?
    Any other register bit will change with this action?
  • 0 in reply to Howard Zou
    TI__Guru**** 166306 points
    Howard,

    Yes. At VBUS POR, the HiZ bit returns to 0. This is required in order for the charger to come out of SHIP mode. When battery remains attached, only HiZ bit and VINDPM (if FORCE VINDPM =0) are reset.

    Regards,
    Jeff