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[FAQ] BQ4050: How to get started with CEDV gauges?

Other Parts Discussed in Thread: GAUGEPARCAL, GPCCEDV

Tool/software:

How do I get started with CEDV gauges? 

  • Production Flow: Compensated End of Discharge Voltage (CEDV)

    1- Identify the gauge based on application. Battery fuel gauges selection.

    2- Calibrate the voltage, current , and temperature measurements using bqStudio

    3- Configure the data memory parameters referencing the Technical Reference Manual (TRM).

        3.1 - Critical data memory parameters that must be configured before cycling the battery.

           3.1-a. EDV2, EDV1 and EDV0 corresponding to 7%, 3% and 0% SOC at room temp. EDV0 corresponds to the cutoff voltage at which the gauge reports 0%.
     
           3.1-b. Taper Current. Recommended values are in between C/10 and C/20 where C indicates the design capacity of the cell.

           3.1-c. Discharge current threshold. Even though it is not required, it is recommended to set this value less than taper current.

           3.1-d. Charge current threshold. This should be less than taper current.

           3.1-e. Quit current. This determines the gauge’s relaxation state. This value should be less that discharge and charge current thresholds.
                     and less than or equal to C/20.

           3.1-f. Design capacity: Rated Nominal capacity of the cell.

           3.1-g. Design voltage: Rated Nominal voltage of the cell.

           3.1-h. Charging voltage: Stated in cell manufacturer datasheet.

           3.1-i. Set FCC Learned Capacity same as Design Capacity. 

                    Note that the gauge will update FCC automatically. However, it must be manually programmed for the *initial* configuration image. 

    4- Most of TI CEDV gauges likely offer fixed EDV or Compensated EDV.

        4.1- Fixed EDV is recommended for when temperature does not vary in the application. For instance, if the gauge will always be used at room
               temperature, then it is easier to manually set the fixed EDV thresholds since the EDV points will mostly be the same on the OCV curve. 

            4.1-a. How to manually calculate EDV thresholds? 
                      

    • You'll have to measure FCC (the gauge provides a coulomb count which you can use or you can integrate your load current over time) from full to empty.
      Use the register log to create a log file. You can then use software like Excel or Numbers to sum up (integrate) the current from a full charge to
      voltage dropping to EDV0.

    • Once you have FCC then you can calculate the actual state of charge in this log file with SOC = 100*RM/FCC for every line in the log file.

    • Look up the voltage for SOC = 7% (=EDV2) and the voltage for SOC = 3% (=EDV1) and write this, together with FCC to the gauge.
      Disable the CEDV option (automatic compensation of EDV) to 0 for testing.


        4.2- However, if temperature is a factor in the application, it is important to know that OCV curve changes with temperature.
               Therefore, user must use the Compensated-EDV algorithm. This algorithm dynamically calculates the EDV thresholds depending
               on temperature and load. 

               For Compensated-EDV, we still recommend you first get fixed EDV working well. This will imply the gauge is mostly configured well. 

               4.2-a. For CEDV algorithm, please reference to Simple Guide to CEDV Data Collection app note. 

               4.2-b. Once the data has been collected, use the GPCCEDV tool to submit the files.

               4.2-c. Program the returned 7 CEDV coefficients (EMF, C0,R0, T0, R1, TC, C1) in the gauge.

               Note: Many users make the mistake of collecting data with a load that differs from the actual load profile. It is highly recommended that
                         user inputs the actual application load profile when collecting data for the GPCCEDV tool. This is to get the best gauging accuracy
                         right away. Note that capacity prediction accuracy gets better over cycling.

                         For instance, if the highest application load is 6A and lowest application load is 1A, then high-rate load is 6A and low-rate load is 1A. 

                                                                        

    5. Extract golden file. This is a good point to save the latest settings.  

    6. Evaluate accuracy at room and low temperature with actual load profile

        6.1 Please allow several cycles for gauging capacity estimations to recover and get better. If after a few cycles issues persists, please contact
              a TI gauge expert using the TI E2E design support forums

    7. Program golden file on multiple units

    8. Perform calibration on each unit ( this step can be avoided if high measurement accuracy isn’t required by  using averaged calibration values from 10 boards in the golden file calibration parameters)

    9. Put device into ship mode