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

3.2.2.2 Single-Channel Configuration

For a 100-kΩ pullup resistor, a single-channel configuration where only one channel is connected is built up. The mechanical switch is turned off. The pullup resistor is 100 kΩ. Then, the broken wire detection is executed. Figure 3-6 shows a scope shot where channel 2 of the scope is connected to the input capacitor CIN of one ISO1211 channel (V_cap) and channel 1 is connected to the OUT pin of the same ISO1211 (ChOut). Figure 3-7 shows a zoom into Figure 3-6.

TIDA-01509 Single Broken Wire Detection, Rpullup = 100 kΩ - V_cap (2), ChOut (1) Figure 3-6 Single Broken Wire Detection, Rpullup = 100 kΩ - V_cap (2), ChOut (1)
TIDA-01509 Zoom into Figure 3-6 - V_cap (2), ChOut (1) Figure 3-7 Zoom into Figure 3-6 - V_cap (2), ChOut (1)

Now the charging of CIN takes only around 3 ms. This amount of time is expected because now the pullup resistor is much smaller compared to before (100 kΩ <=> 800 kΩ). Furthermore, the maximum voltage at the input capacitor is now 23.6 V and the resulting pulse length is 57 µs.

Because fewer components are used, there is less leakage in the system and less current is flowing. Therefore, the voltage drop across the pullup resistor is smaller. In addition, more energy is stored on the capacitor (EC = 1/2 × C × U2), which makes the output pulse longer. Also, while the capacitor is discharged there is additional current flowing through the pullup resistor, which is recharging the capacitor at the same time. This current is again higher for a pullup resistor of only 100 kΩ compared to 800 kΩ.

Figure 3-8 shows a scope shot for the same single-channel configuration. However, now the supply voltage is only 14.9 V. There is still energy stored in the capacitor so that a pulse is generated at the output of the ISO1211. However, due to the lower input voltage, the output pulse is reduced to 15 µs now.

TIDA-01509 Single Broken Wire Detection, V = 14.9 V, Rpullup = 100 kΩ - V_cap (2), ChOut (1) Figure 3-8 Single Broken Wire Detection, V = 14.9 V, Rpullup = 100 kΩ - V_cap (2), ChOut (1)