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BQ25606: The Status output is alternating between high and low levels during charging

Jenny Lu69
Expert 1810 points
Part Number: BQ25606

Hi sir,

In my design, BQ25606 was used to charge a pack of lithium battery(2500mAh), which type is UR16650Z.

But I had encountered some issues now, that the status output is alternating between high and low levels during charging after a few hours, and i'm confused if the lithium is full charged. My circuit as followed, pls give some support.

(R10=240Ω，R11=0Ω，R12=430Ω,R13=0Ω)    0Ω is test resistance. And After plugging in 9V dc, Q1 has been on.

Regards,

Jenny

  • 0
    TI__Mastermind 25800 points

    Hey Jenny,

    What is the rate of oscillation? ~1Hz or variable?

    What is the battery voltage and the BAT pin voltage when this occurs? Do you have a waveform showing transitions?

    Do you have fixed load at the SYS pin? Or does it vary?

    A few things I will mention are:

    Battery cell to BAT pin line/trace impedance can be a factor in something like this where the BAT pin voltage will swing down below the recharge threshold once the charging terminates.

    We typically recommend at least 20uF on the SYS output just for stability of the internal converter.

    Charging termination (what the charger does) is not the same as charging to "full". Only a gauge/fuel IC (i.e. bq27532) can give State of Charge (SOC) approximations. The charger can only terminate charging when the charger current falls below a threshold current called the termination current (ITERM in our charger), so it has no information about the SOC. Termination happens the BAT pin voltage is in the CV region of operation. In other words, when the BAT pin voltage measures to the programmed VSET value, which would be 4.352V in your case (R13 to GND).

    The STAT pin of the charger will oscillate at ~1Hz the charger detects a fault present.

    Regards,

    Joel H