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BQ27427: improper SOC values during charging

Mohamed Aslam
Prodigy 190 points
Part Number: BQ27427
Other Parts Discussed in Thread: BQSTUDIO, BQ27426

Hi all,

I am using BQ27427 in one of our application. We are not getting proper SOC value during charging condition.

Below is the battery parameters:

1. chemical ID : 0x1202 (4.2V)

2. Design capacity (700mAh)

3. Design Energy (2.59 Wh)

During discharge condition, I am getting proper SOC value.

But during charging condition, I am getting full capacity SOC value (99%). And after disconnected the charger, I am getting updated SOC value.

Eg: Before charging, SOC is 85%; During charging SOC is 99%; After charging. SOC is 90%.

Please provide us solution for the issue.

Regards,

Aslam

  • 0
    TI__Mastermind 24741 points

    Hello Aslam, 

    Can you please provide me with the gg and the log file obtained from bqStudio associated with this behavior? 

    Regards, 

    Jonny. 

  • 0 in reply to Jonny
    Prodigy 190 points

    Hi Jhonny,

    I am not using bqStudio to configure the values. I am directly giving I2C commands from the controller.

    I have only changed three configuration values of the fuel gauge, other values are same as default configuration parameter.

     Below are the changed configuration values:

    1. chemical ID : 0x1202 (4.2V)

    2. Design capacity (700mAh)

    3. Design Energy (2.59 Wh)

  • 0 in reply to Mohamed Aslam
    TI__Mastermind 24741 points

    Hello Aslam, 

    In order to refer to the SoC accuracy of the gauge, you will need to configure more parameters and complete a learning cycle. Please refer to the following Quick-Start Guide for bq27426 Fuel Gauge document. This document is for the bq27426, but it can also be applied to the bq27427 in general. 

    Regards, 

    Jonny. 

  • 0 in reply to Jonny
    Prodigy 190 points

    Hi Jhonny,

    Thanks for the suggestion.

    I have gone through the document. And I have configured the below parameters in the fuel gauge.

    1. chemical ID : 0x1202 (4.2V)

    2. Design capacity (700mAh)

    3. Design Energy (2.59 Wh)

    4. Taper rate= design capacity/(0.1*tapper current) = 700/(0.1*30) =233 (0.1 Hr rate).

    5. Terminate voltage = 3200 mV

    6. Design current threshold = C/16.7 = 700/16.7 = 42

    7. Charge current threshold = C/10 = 700/10 = 70

    8. Quit current = C/25 = 700/25 = 28

    But still I am getting full capacity SOC value during charging.

    I have attached our circuit for your reference (R4 and R11 are not populated in the circuit). Please check the circuit and give us solution.

    Regards,

    Aslam

  • 0 in reply to Mohamed Aslam
    TI__Mastermind 24741 points

    Hello Aslam, 

    I recommend ensuring that you successfully complete the learning cycle for this. Please refer to this document on Achieving the Successful Learning Cycle. 

    Regards, 

    Jonny.