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

2.2.1.10 Backup Power Supply

There are three possible power scenarios:

  1. Single or three-phase power available:
    1. The converter supplies all voltages and charges the supercapacitors in a variable time between 1 minute and 21 seconds as first charge, and 36 seconds as successive recharges.
    2. The switching waveform present on the secondary side winding is peak-rectified and is used to disable the inverting buck-boost converter.
    3. At the same time, as the voltage on the supercapacitors is in the range of 4.3 V to 7.8 V, the boost converter is active and delivers 11.5 V. This voltage level, slightly lower than 12 V, is on purpose to avoid delivering current when mains is present. Keeping the boost converter active eliminates the delay due to the device soft start.
    4. When the supercapacitors are charged, a voltage supervisor TL7705A is enabling the flag EOC (end of charge, useful for a digital output to uC) and turning an LED on.
  2. Power unavailable:
    1. Since the boost converter with TPS55330 is always active, the 12-Vp bus droops from 12 V to 11.5 V, keeping all rails alive.
    2. At the same time, both ± 14-V outputs from the flyback converter go to zero and the peak rectified voltage used for the signal Disable goes to zero.
    3. Next, the inverting buck-boost converter, located on the TIDA-010939, starts and supplies ±14 V, which are connected by ORing diodes to the input of the dual LDO, supplying ± 12 V.
    4. The power is delivered until the supercapacitors are discharged below boost UVLO (4.3 V). At this point all rails are off.
  3. Powered from TIDA-010939 with an external 12V supply:
    1. In this scenario, the supercapacitors are not recharged because there is no voltage on auxiliary winding of the flyback.
    2. The 12 V from external power supply on the TIDA-010939 is powering all the rails normally. The inverting buck-boost converter is also supplying ±14 V for dual LDO.