JAJU858 December   2022

 

  1.   概要
  2.   リソース
  3.   特長
  4.   アプリケーション
  5.   5
  6. 1System Description
    1.     7
    2. 1.1 EV Charging Station Challenges
      1. 1.1.1 SAE J1772 or Equivalent Standard Compliant EV Charging Stations
      2. 1.1.2 AC and DC Leakage, Residual Current Detection (RCD)
      3. 1.1.3 Efficient Relay and Contactor Drive
      4. 1.1.4 Contact Weld Detection
    3. 1.2 Key System Specifications
  7. 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 Control Pilot Signal Interface
        1. 2.2.2.1 J1772 Duty Cycle
          1. 2.2.2.1.1 Control Pilot Signal States
          2. 2.2.2.1.2 Control Pilot Signal Circuit
      3. 2.2.3 Relay Drive and Weld Detect
      4. 2.2.4 Residual Current Detection
        1. 2.2.4.1 Auto-Oscillation Circuit
          1.        37
        2. 2.2.4.2 DRV8220 H-Bridge
        3. 2.2.4.3 Saturation Detection Circuit
        4. 2.2.4.4 H-Bridge Controlled by DFF
        5. 2.2.4.5 Filter Stage
        6. 2.2.4.6 Differential to Single-Ended Converter
        7. 2.2.4.7 Low-Pass Filter
        8. 2.2.4.8 Full-Wave Rectifier
        9. 2.2.4.9 MCU Selection
    3. 2.3 Highlighted Products
      1. 2.3.1  UCC28742
      2. 2.3.2  TLV1805
      3. 2.3.3  DRV8220
      4. 2.3.4  ISO1212
      5. 2.3.5  ADC122S051
      6. 2.3.6  TPS7A39
      7. 2.3.7  TPS7A20
      8. 2.3.8  ATL431
      9. 2.3.9  TL431
      10. 2.3.10 TPS563210A
      11. 2.3.11 TPS55330
      12. 2.3.12 TPS259470
      13. 2.3.13 TL7705A
  8. 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 Efficiency and Output Voltage Regulation of TPS563210
        3. 3.3.1.3 Output Voltage Ripple Waveforms
        4. 3.3.1.4 Start, Shutdown, Backup Power, and Transient Response Waveforms
        5. 3.3.1.5 Thermal Performance
      2. 3.3.2 TLV1805-Based Control Pilot Interface
        1. 3.3.2.1 TLV1805 Output Rise and Fall Time
        2. 3.3.2.2 Control Pilot Signal Voltage Accuracy in Different States
      3. 3.3.3 DRV8220-Based Relay and Plug Lock Drive
      4. 3.3.4 ISO1212-Based Isolated Line Voltage Sensing
  9. 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 サポート・リソース
    4. 4.4 Trademarks
  10. 5About the Author

2.2.4 Residual Current Detection

This reference design implements a discrete version of residual current detection (RCD) capable of detecting two types of ground faults, AC current of 30 mARMS and DC current of 6 mA. This detection is enabled utilizing an auto-oscillation circuit along with a receiver filter circuit. For the auto-oscillation circuit, the DRV8220 H-bridge is used to drive the magnetic core in and out of saturation. In addition, a feedback circuit is used to determine when the core reaches saturation and switches the drive coil current in the opposite direction. This enables the design to detect small amounts of DC current with a single toroidal magnetic core. The receive filter stage is used to filter the auto-oscillation driving frequency and signal condition the fault current signal. This filtered signal is captured by the internal ADC of the MSP430 with a sampling rate of 25,000 samples per second. The signal highest and lowest values are stored over 10 ms to determine if the fault type is AC or DC. The AC and DC trip thresholds can be adjusted via software to support different regional specifications. If the stored values are above trip thresholds, the MCU outputs a GPIO high, which is intended to interface with a relay driver to trip the relay. The GPIO returns low when the fault current lowers below an adjustable hysteresis. A summary of the sub-circuits follows for the AC and DC leakage current detection circuit.

Note:

The following RCD description references component designators from the TIDA-010237 schematic. For a more detailed RCD description see the TIDA-010237 user's guide.