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BQ27220: Remaining capacity is changing too slow.

Neha Parmar
Prodigy 30 points
Part Number: BQ27220
Other Parts Discussed in Thread: BQSTUDIO, GPCCEDV, EV2400

Tool/software:

Hello,

We are using BQ27220 to Monitor the SoC (State of Charge) and Voltage of 900 mAh battery, based on the battery specifications and the technical reference manual of BQ27220 we are configuring these values.                       

    Full Charge Capacity :  900 mAh
    Design Capacity :  900 mAh
    Design Voltage :   default : 3700 mV
    Charge Termination Voltage : default : 100 mV

    we are writing these values through I2C interface. Below we have listed the battery specification on which we have done the testing. It is a LiPo battery.
    Battery Chemistry : LiPo
    Nominal Voltage : 3.7 volt
    Design Capacity : 900 mAh
    Max. Charge Current : 450mA
    Standard Charge Current : 180mA
    Discharge Current : 900mA
    Standard Discharge Current : 450mA

     As we didn't use learning cycle to get the configuration data for the fuel gauge, we have configured it on the basis of battery specifications.
     we mainly had changed battery design capacity which is 900mAh, and tried many different configurations but we observed that the value of remaining capacity and SOC is changing too slow.Besides this it shows approximately correct value for SOC when we restart or re-configure any profile value but then it gets to stuck again as it changes remaining capacity too slow. As we are getting accurate values for voltage, and FCC after update.

     So, can you please tell us if we are missing something or there is need for this gauge to go through a learning cycle for accuracy?

  • 0
    TI__Mastermind 27095 points

    Hello Neha,

        Before looking at your gauge I would make sure that your values in the "Register" tab in BQstuido is fill out as you have it in your message above. Also make sure that you have  the right ChemID for your cell in the "Chemistry" tab of BQStudio. 
        Since this device algorithm uses CEDV and not impedance taking you can't perform a learning cycle, rather you would use the GPCCEDV tool that works with BQStudio. Lastly  I would perform a "voltage", "Current" and "temperature" calibration under the "calibration" tab in BQStudio. During the calibration these test are very important to be done right. If your system is not accurate to your needs after doing these steps a chip with Impedance tracking typically provides higher accuracy in determine the SOC of a cell. 


    CEDV:
    https://www.ti.com/tool/GPCCEDV

    CEDV and Impedance Tracking difference:
    https://www.ti.com/lit/an/sluaar3/sluaar3.pdf?ts=1739549550607&ref_url=https%253A%252F%252Fwww.google.com%252F#:~:text=Firstly%2C%20unlike%20coulomb%20counting%20%2FCEDV,for%20long%20periods%20of%20time.



    Regards,
    Alan

  • 0 in reply to Alan Frias
    Prodigy 30 points

    Hello,
    Thank you for your quick reply, we have explored the documentation about all the steps you have mentioned and according to those documentations we came to the following process to configure the gauge, so can you please confirm if it is correct.


    Step 1 : Install bqStudio and connect the hardware (bq27220EVM, EV2300 or EV2400).

    Step 2 : Take logs using bqStudio software utility called GPC Packager by clicking the "Start Log" button (As mentioned in bq27220EVM - 744 user's guide 3.1). 

    Step 3 : Create 3 pairs of log files by using TI’s Battery Management Studio (bqStudio) software with a CEDV evaluation board connected through USB on three different temperatures, typical temperatures for the test are 5°C, 30°C, 50°C. (As mentioned in Simple Guide to CEDV Data Collection for Gauging Parameter Calculator).

                        : Name of files are : Configuration File with parameter (ChemType : 1(LiCoO2))
                                                      : 3 pairs of log files -> hightemp_highrate.csv
                                                                                     -> hightemp_lowrate.csv
                                                                                     -> roomtemp_highrate.csv
                                                                                     -> roomtemp_lowrate.csv
                                                                                     -> lowtemp_highrate.csv
                                                                                     -> lowtemp_lowrate.csv

                         : Data in the file : Time (in seconds elapsed), Voltage (in millivolts), current (in milliamps where discharge current is negative), and direct cell temperature (in degrees  Celsius, one decimal place is acceptable) are recorded and stored as separate columns separated by commas.

                          : This logs are from fully charged state until termination voltage is reached.

    Step 4 : Upload this files on TI Engine(GPC) in the form of zip file.
    Step 5 : Get the CEDV Coefficients from the mail.

    Step 6 : Configure calibration data(ex: CC Offset, board offset, temperature, current and voltage) for the battery pack using bqStudio (As mentioned in bq27220 Calibration guide 3.1).I am also confused if there is any change needed in Data Memory Screen except (As mentioned in bq27220EVM - 744 user's guide 3.2) the parameters used in calibration window(As mentioned in bq27220EVM - 744 user's guide 3.3).
    Step 7 : Program the design parameters to the gauge(Ex. design capacity). 

    Step 8 : Set BATT_ID2 to 1.
    Step 9 : Configure this CEDV Coefficients used for gauging this battery pack.

    Step 10: confirm all the parameters mentioned above by reading SOC.

    Step 11 : After done with the parameters set all the parameters including calibration, configuration and profile to all the gauges used for this battery pack in OTP.

    And please also give information about, how can we confirm if we have the correct ChemID for the battery pack in the "Chemistry" tab of bqStudio, And can we also configure the received CEDV Coefficients directly using I2C of Micro controller?