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

3.4.2 Constant Control Accuracy 12-bit ADC Feedback

For cost-optimized systems, instead of the ADS131M08, use the 12-bit on-chip ADC in the feedback. In each PWM cycle 4 current measurements are taken, which is then averaged over 6 PWM cycles. Figure 3-12, Table 3-2, and Table 3-3 show output current error at different output current and voltage levels. It is observed that with a 12-bit ADC feedback, it is possible to achieve ±0.05% current control accuracy.

GUID-20201020-CA0I-K6HS-HKVN-3NTDRN7W9D8N-low.gifFigure 3-12 Constant-Current Control Accuracy 12-bit ADC Feedback.

Table 3-2 Charge Current Under Different Output Voltage, 12-bit ADC Feedback
VbatteryIset - Charge Mode
0.1 A1 A5 A10 A
0.51.00160.09845.0110.025
11.00160.09845.0110.023
1.51.00160.09845.008910.023
21.0040.09845.007810.023
31.00040.09845.007810.023
41.00040.09845.007810.021
4.51.00040.09725.006610.023
Variation (% FSR)0.012%0.036%0.034%0.04%
Table 3-3 Discharge Current Control With Different Battery Voltage, 12-bit ADC Feedback
VbatteryIset – Discharge Mode
0.1 A1 A5 A10 A
10.09861.00345.022610.05
20.09841.00325.022410.0484
3.10.09821.00285.023410.0448
3.70.0981.0035.021810.0458
40.09821.00365.02310.0466
4.50.09821.00325.022210.0468
Variation (% FSR)0.006%0.008%0.016%0.052%