TIDUF85A August   2024  – December 2024

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1. 1.1 Key System Specifications
  8. 2System Overview
    1. 2.1 Block Diagram
      1. 2.1.1 Subsystems
        1. 2.1.1.1 Arc Detection Channels
          1. 2.1.1.1.1 Isolated Current Measurement
          2. 2.1.1.1.2 Band-Pass Filter
          3. 2.1.1.1.3 Analog-to-Digital Conversion
          4. 2.1.1.1.4 Arc Detection Using Embedded AI Models
        2. 2.1.1.2 Arc Labeling Circuit
          1. 2.1.1.2.1 Isolated String Voltage Measurement
          2. 2.1.1.2.2 Isolated Arc Voltage Measurement With Isolated Comparator
          3. 2.1.1.2.3 Window Comparator for Advanced Labeling
    2. 2.2 Design Considerations
      1. 2.2.1 Current Sensor and Input Stage
      2. 2.2.2 Analog Band-Pass Filter
      3. 2.2.3 Arc-Labeling Circuit
        1. 2.2.3.1 String Voltage Sensing
        2. 2.2.3.2 Arc Gap Voltage Sensing
        3. 2.2.3.3 Differential to Single-Ended Conversion
        4. 2.2.3.4 Window Comparator for Arc Labeling
      4. 2.2.4 Auxiliary Power Supply
      5. 2.2.5 controlCard and Debug Interface
    3. 2.3 Highlighted Products
      1. 2.3.1 TIEVM-ARC-AFE
      2. 2.3.2 TMDSCNCD28P55X – TMDSCNCD28P55X controlCARD Evaluation Module
        1. 2.3.2.1 Hardware Features
      3. 2.3.3 OPA4323 – Quad, 5.5V, 20MHz, Zero-Cross Low-Noise (6nV/√Hz) RRIO Operational Amplifier
      4. 2.3.4 OPA323 – Single, 5.5V, 20MHz, Zero-Cross Low-Noise (6nV/√Hz) RRIO Operational Amplifier
      5. 2.3.5 AMC3330 – ±1V Input, Precision Voltage Sensing Reinforced Isolated Amplifier With Integrated DC/DC
      6. 2.3.6 AMC23C11 – Fast-Response, Reinforced, Isolated Comparator With Adjustable Threshold and Latch Function
  9. 3Hardware, Testing Requirements, and Test Results
    1. 3.1 Signal Chain Verification
      1. 3.1.1 Hardware Requirements
      2. 3.1.2 Test Setup
      3. 3.1.3 Test Results
    2. 3.2 Arc Testing
  10. 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 Documentation Support
    4. 4.4 Support Resources
    5. 4.5 Trademarks
  11. 5About the Author
  12. 6Revision History

2.2.1 Current Sensor and Input Stage

In this reference design, the string current is used to detect an arc fault. Typically, only the AC content is analyzed which allows use of an AC coupled current sensor like a current transformer. Figure 2-2 shows the schematics for the input circuitry of this reference design. There are two input options. Either the onboard CT can be used or a external sensor can be connected to J1 (J2, J3, or J4 for channels 2, 3, or 4). To select the onboard CT, place a jumper on connector J8 between pins 1 and 2. To select the external sensor input place a jumper on J8 between pin 2 and 3.

TIDA-010955 Schematics Current Sensing CircuitFigure 2-2 Schematics Current Sensing Circuit

The CST206-3A was selected as an onboard CT, since this device offers a high saturation limit and allows feed trough of the PV cable without cutting the cable. See Figure 3-2 for saturation testing. The output of the CT is connected to a 300Ω burden resistor R5, which results in a sensitivity of 1V/A. This signal is connected first to RC filter R4 and C1. R75 and D1 implement an overvoltage protection for the gain stage. Footprints for a notch filter are provided with L1 and C21. This notch filter can be used to filter out the inverter switching frequency to prevent saturation of the gain stage. U1 implements a simple gain stage. A gain of 10 is selected since typical arcing signatures have amplitudes up to 100mA or 200mA. These settings result in a voltage of 100mV to 200mV of voltage drop across the R1. The amplified signal is the connected to the filter stage.

For other input voltages or if a external current sensor with a different sensitivity is used the gain can be adjusted by changing R1 and R2.