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BQ25672: Does not operate after short power interruption

Liubomyr Holovatskyi
Prodigy 30 points
Part Number: BQ25672

Tool/software:

In our design we use BQ25672 for 2S Li battery charging and power management.

Issue descruption: after input voltage interruption for several seconds interval, BQ25672RQMR does not operate from adapter.

As AC adapter has a bulk output capacitor, if AC voltage is interrupted, VBUS voltage decreases gradually. If AC recovers when VBUS is ~3.4V, BQ25672RQMR will not operate from adapter.

PG Status: NOT power good, VACstatus: present, Poor Source status: normal.


In case of operating without battery, trere is no SYS voltage for 7 minutes.
Or it needs to wait for ~1 min without AC (to discharge capacitors so that VBUS is below 3.4V) to recover VSYS.

  • 0
    TI__Guru**** 166396 points

    Hi Liubomyr,

    The status and fault registers in REG0x1B through REG0x27 should report the fault.  I suspect the timing of your adapter attach/remove is tripping either poor SRC (fault in REG0x22[4]), which results in 10 min converter turn off, or SYS short, which results in auto EN_HIZ = 1 (REG0x0F[2]).  The 10 min turn off cannot be changed.  The host software can set EN_HIZ back to 0.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Intellectual 470 points

    Hi Jeff.

    We'll check both suggestions, thanks. If it's related to source detection, could you provide us with some recommendations on the timing for attaching and removing our adapter, so we can determine how to work around this issue on our end?

    Regards, Vasyl.

  • 0 in reply to Vasyl Vorobei
    TI__Guru**** 166396 points

    Hi Vasyl,

     Does the fault flag in REG0x22[4] report a previous Poor SRC, resulting in converter shutdown for 7-11 min?  Does EN_HIZ bit =1 in REG0x0F[2]?  Since VBUS has to fall below 3.4V to fix, it could be either.  The SYS short timing is shown below:

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 30 points

    Hello Jeff,

    Yes, EN HiZ bit is set.

    See also other settings:

    Clearing EN HiZ solves the issue, but in case of no battery operation host controller will not be able to clear it, as it has no power.

  • 0 in reply to Liubomyr Holovatskyi
    TI__Guru**** 166396 points

    Hi Liubomyr,

    I suggest reviewing the app note below.  It addresses a similar issue when solar panel voltage drops and no battery is attached.

    https://www.ti.com/lit/pdf/sluab26

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Intellectual 470 points

    Hi Jeff.

    Thanks for the suggestion, we'll test the circuit from the app note.

    It is still unclear why we observe the false poorsrc detection in our system. For now, we're pretty sure that our AC-DC works as intended and poses no issues with voltage or power ratings for the PMIC.

    I presume that, since the SLUAB26 circuit is designed for a weak source (as a solar panel), it may introduce additional negative cases with a partially damaged AC-DC converter, which are currently covered by source detection. So it's still more preferable for us to understand which part of our design conflicts with the BQ25672 internal logic.

    Regards, Vasyl.

  • 0 in reply to Vasyl Vorobei
    TI__Guru**** 166396 points

    Hi Vasyl,

    Normal startup timing is below:

    Poor source detect occurs immediately after REGN comes up.  If poor source fails, the charger goes HiZ for ~10min and tries again.  If not poor source but SYS falls < 2V, the charger retires to get SYS voltage up 7 times with the timing below.

    If SYS does not come up, the charger sets EN_HIZ bit =1.  Either a full power cycle or I2C write or VACx pin toggle with VAC>UVLO per app note above is required to reset EN_HIZ bit to 0.

    Regards,

    Jeff