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bq25101H Unstable charging current

Tsukui Yusuke
Guru 21930 points
Other Parts Discussed in Thread: BQ25101H, BQ25101

Hi,

I have got a question about the charging current of bq25101H from the customer.
Can you check the attached waveform and customer circuit?
bq25101H.zip

Customer is measured in terms of ISET voltage.
Could you tell me advice about the cause of charge current .
Does this Issue is related additional circuit of ISET?



Best Regards,
Yusuke / Japan Disty

  • 0
    TI__Expert 7730 points

    The additional circuit is needed when the fast charging current is below 50mA,so it is recommended in this application.

    The unusual performance of the current in CV mode is likely to be caused by the line resistance between battery and the OUT pin of the IC. I have also seen the similar behavior when customer is using a high impedance current meter to measure the current. Can you let me know how did the customer measure the current?

    BTW, what is the 2.2k ohm  resistor on /CHG pin doing?

    Thanks,

    Wenjia

  • 0 in reply to Wenjia Liu
    Guru 21930 points

    Dear Wenjia Liu-san

    Thank you for reply.
    I let a customer try additional circuit.
    I report it after asking a customer method for measurement.

    2.2k ohm  resistor on /CHG pin was my mistake,so please ignore them.

    Best Regards,
    Yusuke / Japan Disty

  • 0 in reply to Tsukui Yusuke
    Guru 21930 points

    Hi Wenjia-san,

    Customer is reading the voltage of ISET pin in the logger. (IST pin- logger line is about 1m.)
    Customer have been translated the measured voltage to the charging current.
    Could you advice about the only issue①.




    Customer added the RC circuit. However, the problem did not resolve.
    I have got the following question from customer.

    ◇Why bq25101H will require RC circuit when the charging current is small(50mA)?
    ◇Could you tell me the calculation method of the RC circuit.
    ◇This issue occurs only in H version of the IC.(Condition is using the same circuit and battery)
    　  Is the difference between bq25101H and bq25101 only the charge voltage?
         Please tell me other differences.

    Best Regards,
    Yusuke / Japan Disty

  • 0 in reply to Tsukui Yusuke
    TI__Expert 7730 points
    1. The RC circuit is used to add the compensation to ISET circuit at low current due to the parasitic capacitance at this pin.
    2. The RC value was calculated based on design simulation.
    3. 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

    As you mentioned that customer was using the same battery, I would expect it is the 4.35V battery. Bq25101 is a 4.2V charger so when the battery voltage is close to 4.2V, the bq25101 will stop charging but it is not yet in CV for the 4.35V battery. Therefore bq25101 didn't have this issue.

    Can customer measure the line resistance between OUT pin and the real battery? Can they try floating TS and measure the current again?

    Thanks,
    Wenjia
  • 0 in reply to Wenjia Liu
    Guru 21930 points

    Hi Wenjia-san,

    Thank you for your support.
    Could you tell me more specific about your answer 1.2.?
    ◇When I do not add RC circuit, what kind of problem happens?
    ◇Should I change RC depending on the situation(battery spec, circuit pattern)?
        Will you calculate the RC if I inform condition?

    I confirm following your advice to customer. I will report to you later.
    ・Can customer measure the line resistance between OUT pin and the real battery?
    ・Can they try floating TS and measure the current again?

    I want to show you charging current graph of the customer, so please email me directly.
    My e-mail address is: tsukui-y@clv.macnica.co.jp

    Best Regards,
    Yusuke / Japan Disty