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Ploblem of bq25100

Satoshi
Guru 19495 points
Other Parts Discussed in Thread: BQ25100

A customer is estimating bq25100 by the following circuit.

When charging , the battery voltage is changing about 300 mV.

※Thermistor is same as datasheet recommendation(10-k NTC β = 3370).

　　Battery is 210mAh.

 

A waveform is the following.

※Yellow: The battery voltage

　　Red: DC after the resister divide.

I think a battery detecting routine, because the cycle of the change is 55ms.

When without a thermistor, it doesn't change(normally move) and steady voltage.
(TTDM mode?)

When there is a battery when  is seen, Datasheet "8.4.6 Battery Detect Routine" writing that it'll be this routine at all except for TTDM.

But moving that a thermistor is connected state.

 

Please let me know the way to make it normal movement in the state with a thermistor.

 

Best regards,

Satoshi

  • 0
    TI__Expert 7730 points
    Is the IC charging normally when you saw the oscillation at VOUT? Can you also capture the charging current and ISET voltage?
    The waveform shows the VOUT is jumping between ~3.9V to 4.2V, which looks like there's no battery connected.

    Thanks,
    Wenjia
  • 0 in reply to Wenjia Liu
    Guru 19495 points

    Dear Wenjia Liu-san

    Thank you for reply.

    I attached waveform of battery voltage and Iset voltage.

    【Additional Information】

    ・Charge current is 40mA.

    ・When started near full charge (4.2V), there's a low probability of this problem occurring.

    ・When measured to use IC tester, there's a high probability of this problem occurring.

     (I think that it depend on internal resistance)

     

    Best regards,

    Satoshi

  • 0 in reply to Satoshi
    TI__Expert 7730 points

    Hello Satoshi-san,

    I think this might be caused by the line resistance between the OUT pin of the device and the real battery. Because of the voltage drop over the line, the OUT pin voltage is higher than the real battery so the IC will terminate charging even if the real battery voltage is below 4.2V. Once the charging is terminated, the current drops to zero so the voltage drop is also reduced to zero. Now without the voltage drop, OUT pin voltage is the same as the real battery so the charging is started again. I think this is the reason why you can see that ISET is on and off.

    Can you measure the resistance between OUT pin and the battery?

    Thanks,

    Wenjia

  • 0 in reply to Wenjia Liu
    Guru 19495 points

    Dear Wenjia Liu-san

    Thank you for reply.

     

    bq25100 moved normally without a thermistor, is this also related to the factor?

    Is the cause by the quality of the thermistor considered?

    Line resistance between OUT pin and the battery, customer checking now.

    If I get data, it'll be reported.

    Best regards,

    Satoshi

  • 0 in reply to Satoshi
    TI__Expert 7730 points
    When the thermistor is removed, the IC enters TTDM mode in which the battery detection and termination are both disabled. If the issue was caused by termination as what I guessed, then removing thermistor will recover the issue. However, the root cause may still be the line resistance.

    Thanks,
    Wenjia
  • 0 in reply to Wenjia Liu
    Guru 19495 points
    Dear Wenjia Liu-san

    Thank you for reply.

    About the resistance value to which a problem occurs, when Vout doesn't drop to VO_HT (REG), normal operation.
    Is it correct?

    Sorry for additional question, please let me know about Datasheet Figure-23.

    ・I think that bq25100 decision OK or NG after 25ms.
    On this time, Is voltage measurement after "Voutreg:3.9V→4.2V"?
    　On decision battery voltage, is bq25100 charge disable?

    Best regards,
    Satoshi
  • 0 in reply to Satoshi
    TI__Expert 7730 points
    Hello Satoshi-san,

    During the battery detection, the IC will read the voltage first for 25mS and see if it is less than 4.1V , and then sink current for 25mS to regulate the VOUT to 3.8V. The IC is measuring the voltage all the time and only when the battery voltage can be set to both above 4.1V and below 3.9V, it will indicate no battery connection.

    The charging is NOT disabled during battery detection.

    Thanks,
    Wenjia