TIDUEY0 November   2020

 

  1.   Description
  2.   Resources
  3.   Features
  4.   Applications
  5.   5
  6. 1System Description
    1. 1.1 Li-ion Battery Formation
    2. 1.2 Key System Specifications
  7. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 High-Resolution PWM Generation
      2. 2.2.2 Feedback Controller
      3. 2.2.3 Multiphase Configuration
      4. 2.2.4 Current and Voltage Feedback
      5. 2.2.5 Delta-Sigma ADC Clock Frequency Tuning
      6. 2.2.6 Minimize Crosstalk Error With a Differential ADC
      7. 2.2.7 Overcurrent Protection
    3. 2.3 Highlighted Products
      1. 2.3.1 TMS320F280049
      2. 2.3.2 ADS131M08
      3. 2.3.3 INA821
  8. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
    2. 3.2 Software
    3. 3.3 Test Setup
    4. 3.4 Test Results
      1. 3.4.1 Constant Control Accuracy ADS131M08 Feedback
      2. 3.4.2 Constant Control Accuracy 12-bit ADC Feedback
      3. 3.4.3 Constant-Voltage Control Accuracy
      4. 3.4.4 CC, CV Transformation
      5. 3.4.5 Constant-Current Transient Response
      6. 3.4.6 Charge to Discharge Mode Transition
  9. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
    2. 4.2 Tools and Software
    3. 4.3 Support Resources
    4. 4.4 Trademarks
  10. 5About the Author

3.4.1 Constant Control Accuracy ADS131M08 Feedback

The current accuracy depends on the current-sensing resistor, the gain, offset, and drift of the current amplifier, INA821, and TLV07 devices. These parameters vary from device to device. To achieve good current-control accuracy, the total gain and the offset of the designed circuit must be calibrated. Figure 3-11 shows current error after calibration at room temperature with ADS131M08 in the feedback. It can be seen that error increases at high output current > 8 A. This is due to heating of the current-sense resistor at higher output current. This error can be reduced by using smaller current-sense resistors such as 2 to 3 mΩ for 10-A output current.

GUID-20201020-CA0I-GWWW-LZ6K-XFZGGBHTXX45-low.gifFigure 3-11 Constant-Current Control Accuracy ADS131M08 Feedback.

Current feedback noise may change the average output current with variation in battery voltage. Table 3-1 shows output current under different battery voltage and current settings. The test data shows that variation in battery voltage has very little effect on the current.

Table 3-1 Output Current Under Different Battery Voltage and Current Settings
VbatIset
0.01 A0.1 A1 A6 A10 A0.01 A0.1 A1 A6 A10 A
Charge ModeDischarge Mode
0.50.01030.10031.00076.00110.0010.010.11.00036.0003-
10.01030.10031.00076.00110.00070.010.10031.00036.00039.9993
20.01030.10031.00076.000710.00030.010.1003169.9993
30.01030.10031.00076.0007100.010.1169.999
40.01030.11.00076.00079.99970.010.1169.999
50.01030.11.00076.0019.99970.010.1169.999
Variation (% FSR)00.003%00.003%0.013%000.003%0.003%0.003%