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BQ24133: The battery voltage gets fluctuation once 3 cell battery fully charge reached. The STAT also starts blinking.

YI HAO
Prodigy 60 points
Part Number: BQ24133

Before very closing to battery fully charged, everything is normal. But once the battery fully charged, the battery voltage gets fluctuation. It is about 12.06 to 12.56V jump. The STAT also starts blinking. At this time, if drain the battery and turn off the board quickly. The battery voltage gets stable to about 12.5V. 

It is same, no matter if turn/off the load of bq24133. The strange thing is the battery voltage is still fluctuation even the external power removed. Just the fluctuation amplitude gets smaller in this case.

  • 0
    TI__Guru*** 143950 points
    Hi BayValley,

    What is the impedance from the BQ24133 SRN pin to the battery itself? What is your termination current setting? If you increase or decrease the termination current does this effect get worse or better?

    Regards,
    Jeff
  • 0 in reply to Jeff F
    Prodigy 60 points

    Hi Jeff,

    Thanks for your reply.

    The SRN connects to BAT directly. Correct? It is connect to BAT terminal directly. The impedance is too small.

    When board turn on, the charge current is set 0.45A, so the termination current is 45mA.

    When board turn off, the charge current is set to 1.6A, the termination current is 160mA.

    Fluctuation voltage observed for both cases. 

    Regards,

    BayValley

  • 0 in reply to YI HAO
    TI__Guru*** 143950 points
    Hi BayValley,

    With power attached and the battery charging, I can explain the fluctation and STAT blinking as a highly resistive connection to the battery or high impedance battery as the charger goes into and out of termination. However, I do not understand how the battery voltage can fluctuate if there is no input power. The charger goes into HiZ mode with no power at its input so it cannot affect battery voltage. The only circuity that is the PMOS FET drive by /BATDRV. Where are you measuring the battery voltage? Is there a system load that is fluctuating at the same frequency?

    Regards,
    Jeff