TIDUF04A December   2022  – December 2025

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1.     8
    2. 1.1 EV Charging Station Challenges
      1. 1.1.1 Efficient Relay and Contactor Drive
      2. 1.1.2 Contact Weld Detection
    3. 1.2 Key System Specifications
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 Isolated AC/DC Power Supply Design
        1. 2.2.1.1  Input Bulk Capacitance and Minimum Bulk Voltage
        2. 2.2.1.2  Transformer Turns-Ratio, Primary Inductance, and Primary Peak Current
        3. 2.2.1.3  Transformer Parameter Calculations: Primary and Secondary RMS Currents
        4. 2.2.1.4  Main Switching Power MOSFET Selection
        5. 2.2.1.5  Rectifying Diode Selection
        6. 2.2.1.6  Output Capacitor Selection
        7. 2.2.1.7  Capacitance on VDD Pin
        8. 2.2.1.8  Open-loop Voltage Regulation Versus Pin Resistor Divider, Line Compensation Resistor
        9. 2.2.1.9  Feedback Elements
        10. 2.2.1.10 Backup Power Supply
        11. 2.2.1.11 Supercapacitor Selection
        12. 2.2.1.12 Supercapacitor Charger Design
      2. 2.2.2 Relay Drive and Weld Detect
    3. 2.3 Highlighted Products
      1. 2.3.1 UCC28742
      2. 2.3.2 DRV8220
      3. 2.3.3 ATL431
      4. 2.3.4 TL431
      5. 2.3.5 TPS55330
      6. 2.3.6 TPS259470
      7. 2.3.7 TL7705A
  9. 3Hardware, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
    2. 3.2 Test Requirements
      1. 3.2.1 Power Supply Test Setup
      2. 3.2.2 Weld Detect Test Setup
    3. 3.3 Test Results
      1. 3.3.1 Isolated AC/DC Power Supply Based on UCC28742
        1. 3.3.1.1 Efficiency and Output Voltage Cross Regulation
        2. 3.3.1.2 Output Voltage Ripple Waveforms
        3. 3.3.1.3 Start, Shutdown, Backup Power, and Transient Response Waveforms
        4. 3.3.1.4 Thermal Performance
      2. 3.3.2 DRV8220-Based Relay Drive
      3. 3.3.3 Isolated Line Voltage Sensing
  10. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 Bill of Materials
    2. 4.2 Documentation Support
    3. 4.3 Support Resources
    4. 4.4 Trademarks
  11. 5About the Author
  12. 6Revision History

3.2.2 Weld Detect Test Setup

An overview of the weld detect test setup follows:

  • The system checks for the AC signal through the comparator U11 when the relay is open. A normal (unwelded) condition means there are no output pulses.
  • The system checks for the AC signal through the comparator U11 when the relay is closed. A normal (AC present) condition means there are output pulses.

Complete the following work before powering the TIDA-010239 board.

  • Connect the R_ENABLE (J9, pin 9) to external 3.3 V to enable the K1 relay at power up.
  • Connect an isolated HV oscilloscope probe 1 to LINE1_IN (TP1). Connect the probe 1 reference clip to neutral (TP5).
  • Connect oscilloscope probe 2 to RELAY_CHECK (TP16). Connect the probe 2 reference clip to PGND (TP22).
  • Connect oscilloscope probe 3 to the comparator input (TP18). There is no need to connect the probe 3 reference clip.
  • Connect oscilloscope probe 4 to Ref_0.2V (TP21). There is no need to connect the probe 4 reference clip.

Supplying power to the board for testing:

  • Apply external 3.3 V to the connector J9 pin 6 and external 5 V to pin 5 of the J9 connector.
  • Connect GND of the external power supply to one of the ground pins of the J9 connector (pin 7, 8, 13, 14, 17) or to one of the GND test points (TP8, TP9, TP22).
  • The measurement can be repeated with the relay open by disconnecting the R_ENABLE from 3.3 V.