TIDUDI9A January   2018  – May 2025 ISOM8610

 

  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
    2. 2.2 Highlighted Products
      1. 2.2.1 ISO121x
      2. 2.2.2 SN74LV165A
      3. 2.2.3 SN74LVC1GU04
      4. 2.2.4 TVS3300
      5. 2.2.5 ISOM8600
    3. 2.3 System Design Theory
      1. 2.3.1 Digital Input Stage
      2. 2.3.2 Broken Wire Detection
        1. 2.3.2.1 Case 1: Wire Intact and Input State '1'
        2. 2.3.2.2 Case 2: Wire Intact and Input State '0'
        3. 2.3.2.3 Case 3: Broken Wire
      3. 2.3.3 Readout of Digital Outputs
  9. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Required Hardware and Software
      1. 3.1.1 Hardware
      2. 3.1.2 Software
    2. 3.2 Testing and Results
      1. 3.2.1 Test Setup
      2. 3.2.2 Test Results
        1. 3.2.2.1 Group-Channel Configuration
        2. 3.2.2.2 Single-Channel Configuration
      3. 3.2.3 Conclusion
  10. 4Design Files
    1. 4.1 Schematics
    2. 4.2 Bill of Materials
    3. 4.3 PCB Layout Recommendations
      1. 4.3.1 Layout Prints
    4. 4.4 Altium Project
    5. 4.5 Gerber Files
    6. 4.6 Assembly Drawings
  11. 5Software Files
  12. 6Related Documentation
    1. 6.1 Trademarks
  13. 7About the Author
    1. 7.1 Acknowledgments
  14. 8Revision History

3.2.3 Conclusion

The broken wire detection works as expected. However, several observations need to be considered when implementing the broken wire detection.

The higher the pullup resistor to 24 V, the lower the maximum voltage at CIN. Also, consider the leakage current through protection elements and the capacitor. For example:

  1. 100-kΩ pullup, single-channel configuration → V(CIN)max = 23.6 V; 800-kΩ pullup, group-channel configuration → V(CIN)max = 22.6 V
  2. The higher the pullup resistor is to 24 V, the shorter the resulting output pulse → less energy stored in the input capacitor, less (recharging) current flowing through pullup resistor to the ISO121x during discharge
  3. The lower the supply voltage of the switch, the shorter the resulting output pulse → less energy stored on the input capacitor, low-level threshold is reached quicker
  4. The higher the capacitance of the input capacitor, the longer the resulting output pulse → more energy stored in the input capacitor
Note:

In general, it is important to choose an opto-emulator switch that turns on and off quickly. If the opto-emulator switch turns on too slow, CIN will already be discharged too much before the ISO121x has a solid GND connection. Then, no output pulse is created.