TIDUFI7 May   2026

 

  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 Design Considerations
    3. 2.3 Highlighted Products
      1. 2.3.1 ADS125H18
      2. 2.3.2 MSPM0G5117
      3. 2.3.3 TXE8116
      4. 2.3.4 ISO6441
      5. 2.3.5 LM5180
      6. 2.3.6 UCC33420
      7. 2.3.7 TPS7A2050
      8. 2.3.8 TLV709A33
  9. 3System Design Theory
    1. 3.1 Power Supply
      1. 3.1.1 24V Input Power Path
      2. 3.1.2 USB Power Path
      3. 3.1.3 Non-isolated MCU Power
      4. 3.1.4 Isolated ADC and Peripheral Power
    2. 3.2 Analog Input Ports
      1. 3.2.1 Analog Input Port and Protection
      2. 3.2.2 Voltage and Current Mode Selection
      3. 3.2.3 Current Measurement Path
      4. 3.2.4 Voltage Measurement Path
      5. 3.2.5 Channel Configuration
    3. 3.3 Digital Control and Data Acquisition Subsystem
      1. 3.3.1 Microcontroller Platform
      2. 3.3.2 Precision ADC
      3. 3.3.3 Shared SPI Bus and Chip-Select Forwarding
      4. 3.3.4 I/O Expander
      5. 3.3.5 Optional External Reference
  10. 4Hardware, Software, Testing Requirements, and Test Results
    1. 4.1 Hardware Requirements
      1. 4.1.1 PCB Overview
      2. 4.1.2 Connector Description
        1. 4.1.2.1 Power Connectors
        2. 4.1.2.2 Input Connectors
    2. 4.2 Test Setup and Test Results
      1. 4.2.1 ADS125H18 General Configuration
      2. 4.2.2 Offset Test
        1. 4.2.2.1 Test Setup
        2. 4.2.2.2 Test Results
          1. 4.2.2.2.1 Voltage Input Mode
          2. 4.2.2.2.2 Current Input Mode
      3. 4.2.3 System Accuracy Error and Noise Performance Test
        1. 4.2.3.1 Calculation Method
        2. 4.2.3.2 Test Setup
        3. 4.2.3.3 Test Results
          1. 4.2.3.3.1 Voltage Input Mode
          2. 4.2.3.3.2 Current Input Mode
      4. 4.2.4 Input Protection Test
        1. 4.2.4.1 Test Setup
        2. 4.2.4.2 Test Results
  11. 5Design and Documentation Support
    1. 5.1 Design Files
      1. 5.1.1 Schematics
      2. 5.1.2 BOM
      3. 5.1.3 PCB Layout Recommendations
        1. 5.1.3.1 Layout Prints
    2. 5.2 Tools and Software
      1. 5.2.1 Tools
      2. 5.2.2 Software
    3. 5.3 Documentation Support
    4. 5.4 Support Resources
    5.     Trademarks
  12. 6Revision History
  13. 7About the Author

2.3.1 ADS125H18

The ADS125H18 is a high-performance, 24-bit multiplexed delta-sigma (ΔΣ) ADC for precision multi-channel data acquisition in industrial systems. The device integrates an input multiplexer, a precision voltage reference, diagnostic features, and resistor-divider inputs that support up to 20V common-mode signals, which reduces external component count in high-channel-density analog input modules.

The ADS125H18 supports a CS (chip-select) forwarding feature, in which an ADC GPIO can be used to control the CS pin of a secondary device. The CS forwarding feature allows the ADC to assist in managing SPI transactions with external companion devices. As a result, the number of signals that must cross the isolation barrier is reduced, avoiding additional dedicated isolator channels for separate chip-select signals.

In this design, the ADS125H18 serves as the main data converter for the 8-channel analog input front end. The integrated multiplexer, flexible conversion modes, high common-mode input capability through the resistor-divider inputs, and diagnostic capability make the ADS125H18 an excellent choice for PLC and DCS analog input modules that require accurate measurement, efficient channel scanning, and compact implementation over the –40°C to 125°C temperature range.