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BQ25185: BQ25185 not charging the battery according to ISET value.

Ahmed Ali
Prodigy 80 points
Part Number: BQ25185

Tool/software:

Dear TI team,

I hope you are doing well. I have attached my schematics for the BQ25185. I am facing the issue that the battery is not being charged according to the ISET value, which is 300mA. My LiPo battery is at 3.7V, and the charging current fluctuates from 70 to 160mA. I am measuring the current through DMM.
Everything is working according to the datasheet except the charging current. Please also point out any mistakes in the design, if there are any.
Please provide instant support on this matter.

I am looking forward to hearing back.

Regards,
Ahmed Ali

Also, check the circuit for +5V to see whether it is okay.

  • +1
    TI__Expert 7980 points

    Hi Ahmed,

    I've reviewed your BQ25185 schematic and it looks good. I don't see any issues.

    What are STAT1 and STAT2 while this issue occurs?

    Also, are you testing with a real battery or an electronic load? Is the charge current continuously fluctuating between 70mA and 160mA? You may need to add a bulk cap (e.g., 1000uF) in parallel with BAT and your BAT supply to smooth out any oscillations.

    Best regards,

    Alec

  • 0 in reply to Alec Lehman
    Prodigy 80 points

    Hi Alec,

    I am testing it with a real battery of 1s LiPo 7000mAh. Yes, the current continuously fluctuates. 

    The STAT1 LED is off, and the STAT2 LED is on.

    Ok, I will add the bulk capacitor to test it out.

    I also performed one more test on my separate board by halving the resistance on the ISET pin and got a charging current of 300 to 330mA.

    I am looking forward to hearing back.

    Regards,
    Ahmed Ali

  • +1 in reply to Ahmed Ali
    TI__Expert 7980 points

    Hi Ahmed,

    I only recommend using a bulk cap if testing with an electronic load. With a real battery, it shouldn't be necessary.

    Thanks for confirming STAT1 is low and STAT2 is high. This indicates that charging is in progress and no faults are present.

    How much current is your system load drawing? It's possible that the device is in DPPM and is reducing the charge current to prioritize powering the system load. Also, what is your input current while this issue occurs?

    Are you able to disconnect your system load and see if the charge current goes to its expected value?

    It's not expected that the charge current will exceed the setting programmed by the ISET resistor.

    Best regards,

    Alec

  • 0 in reply to Alec Lehman
    Prodigy 80 points

    Hi Alec,

    Thanks a lot for your support. I was able to troubleshoot the main issue, which was in my ammeter, which was not reading the current properly. I changed the ammeter and the current was exactly according to the ISET pin.

    The circuit works perfectly well. 

    Regards,
    Ahmed Ali

  • 0 in reply to Alec Lehman
    Prodigy 80 points

    Hi Alec,

    I have another question: How much current can be drawn from VSYS when ISET is set at 300mA?

    Please respond as soon as possible. 

    Thanks,
    Ahmed Ali

  • 0 in reply to Ahmed Ali
    TI__Expert 7980 points

    Hi Ahmed,

    I'm glad to hear you found the issue with your ammeter.

    Ahmed Ali said:
    I have another question: How much current can be drawn from VSYS when ISET is set at 300mA?

    Just to clarify, the amount of current the system can draw is not limited by the fast charge current setting.

    The BQ25185 includes a feature called DPPM (dynamic power path management), which reduces the charging current when the system voltage drops below the VDPPM threshold due to the sum of the charging and system currents exceeding the input current limit. If the charging current is reduced to zero and VSYS drops below VBAT - VBSUP1 (where VBSUP1 is 40mV, typical), the battery begins discharging to supplement the adapter in supplying current to the system. See section 8.3.2. of the datasheet for more details.

    Best regards,

    Alec