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

1 System Description

This reference design shows a compact implementation of 16 isolated digital input channels using TI's new ISO121x devices, a single- (ISO1211) and dual- channel (ISO1212), isolated, 24-V digital input receiver. The design is split into two groups of eight channels each. Every group is built up out of three dual-channel ISO1212 and two single-channel ISO1211 devices.

A broken wire detection can be executed using only one additional opto-emulator switch for each channel. This design does not need any other adjustments to the circuitry.

The opto-emulator switch disconnects the field ground of the ISO121x devices for a short time and connects it again afterwards. This results in a pulse at the output pin of the ISO121x depending on the status of the wire—broken or connected. This pulse even works for logic '0' input signals if the input signal is coming from a high-side switch with a pullup resistor.

For this functionality, no secondary-side supply is needed, which gives a unique benefit to digital inputs built with the ISO121x compared to regular digital inputs that need an additional isolated power supply on the field input side for broken wire diagnostic.

For an easy and quick evaluation, this reference design can be plugged onto the MSP430FR5969 LaunchPad or any other TI LaunchPad with the same SPI pinout. The LaunchPad also supplies power to the system.

Furthermore, this reference design can be used as a regular 16-channel digital input module. The ISO121x device provides an accurate current limit for digital inputs, enabling a power dissipation of less than 1 W for 16 inputs channels for input signals of 24 V. For more information about this, see the Sub 1-W, 16-Channel, Isolated Digital Input Module Reference Design.