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

2.2.2 Analog Band-Pass Filter

Figure 2-3 shows the filter stage consisting of an OPA4323, a 4-channel operational amplifier. U5A and U5B form a low-pass filter with a cutoff frequency at 100kHz. U5C and U5D form a high-pass filter with a cutoff frequency of 30kHz. In combination, this forms a band-pass filter with a pass band of 30kHz to 100kHz. The split topology of low-pass plus high-pass filters is selected to make it easy to adjust upper and lower levels of the band-pass filter separately. U5D also allows for an additional gain by adjusting R153 and R154. This can be used to introduce further gain after the filtering.

TIDA-010955 Schematics 8th Order Analog Band-Pass Filter Figure 2-3 Schematics 8th Order Analog Band-Pass Filter

The two most important specifications of an amplifier in an active filter application are Gain-Bandwidth-Product (GBW) and slew rate (SR).The minimum requirements for GBW and SR are given in Equation 1 and Equation 2.

Equation 1. GBWmin= 100 × G× fc
Equation 2. SRmin= 2 × π × fc ×VP-P

where

  • G = closed-loop gain
  • fc= cutoff frequency of the low-pass filter
  • VP-P= peak-to-peak output voltage

With the values of G = 1, fc = 100kHz, and VP-P = 5V; a minimum GBW of 10MHz and a minimum slew rate of 3.14V/μs are calculated. With a GBW of 20MHz and a slew rate of 10V/μs, the OPA4323 fulfills these criteria and allows for some head room if a higher frequency band is desired. The transfer function is validated in the test results LINK. The output of the filter stage is connected to an internal ADC of the C2000 MCU. Populating R30 and removing R27 allows bypass of the analog filter stage.

For channel 3 and channel 4, only a 2nd order low-pass and 2nd order high-pass is implemented, as shown in Figure 2-4.

TIDA-010955 Schematics 4th Order Analog Band-Pass Filter Figure 2-4 Schematics 4th Order Analog Band-Pass Filter

Therefore, U8A and U8D are just implementing a voltage follower and are not required. This is done to allow comparison between a 4th order band-pass on channels 3 and 4 and an 8th order band-pass on channels 1 and 2. In case 4 similar channels are desired, the resistors and capacitors can be adjusted.