TIDU858C March   2015  – May 2021

 

  1.   Description
  2.   Resources
  3.   Features
  4.   Applications
  5.   5
  6. 1System Description
    1. 1.1 Binary Inputs or Digital Inputs
      1. 1.1.1 Binary Input Application Functionality
      2.      Common Specifications
    2. 1.2 Approaches to Binary Input Module Design
      1. 1.2.1 ADC Versus MCU Based Binary Input Module (BIM)
    3. 1.3 Measurement of Wide Inputs With Programmable Thresholds
  7. 2Design Features
    1. 2.1 Electrical Specifications
    2. 2.2 Block Diagram
      1. 2.2.1 Analog-to-Digital Converter (ADC)
        1. 2.2.1.1 ADS795x SAR ADC Family
      2. 2.2.2 Protection and Signal Conditioning
      3. 2.2.3 Digital Isolator
        1. 2.2.3.1 Host (SPI) Interfacing Using the ISO6741
      4. 2.2.4 DC Power Supply Isolator
      5. 2.2.5 Design Alternative: ADC With Digitally Programmable Threshold
        1. 2.2.5.1 ADS7128 SAR ADC With Programmable Threshold
        2. 2.2.5.2 I2C Interfacing Using the ISO1640 and Optional Altert Interface Using ISO7710
  8. 3Circuit Design and Component Selection
    1. 3.1 Analog-to-Digital Converter (ADC)
    2. 3.2 Input Signal Conditioning
      1. 3.2.1 Voltage Divider
      2. 3.2.2 TLV6002 Operational Amplifier
    3. 3.3 Isolated Interface
    4. 3.4 Isolated DC Power Supply
      1. 3.4.1 Reinforced Power Isolator: UCC12050 High-Efficiency 500-mW DC/DC Converter
    5. 3.5 Enhancements
  9. 4Testing
    1. 4.1 Test Setup and Connection Diagram
    2. 4.2 Test Data
      1. 4.2.1 Voltage Measurement Accuracy Testing
    3. 4.3 Test Results Summary
  10. 5Design Files
    1. 5.1 Schematics
    2. 5.2 Bill of Materials
    3. 5.3 Altium Project
    4. 5.4 Gerber Files
  11. 6References
  12.   Trademarks
  13. 7About the Author
  14. 8Revision History

2.2.5 Design Alternative: ADC With Digitally Programmable Threshold

In applications requiring basic isolation and minimum off-the-shelf processing, consider using the ADS7128 (12-bit, 8-channel SAR ADC), ISO1640 (2-channel bidirectional I2C digital isolator), and ISO7710 (1-channel digital isolator for the ALERT function).

The ADS7128 ADC (see Figure 2-2) features an analog watchdog, enabling the use of a per channel programmable threshold. Individual thresholds can be programmed to alert the host MCU when a binary input reaches a desired voltage level, freeing the host to do operations elsewhere until notified, for increased processor bandwidth. The ISO1640 and ISO7710 digital isolators support I2C interfacing and a 3-kVRMS isolation rating (basic isolation).

Unlike a typical optocoupler solution, a module implementing this threshold detection technology will have the ability to support AC/DC inputs of varying voltage levels with a single board. A user can easily program their desired threshold values and duplicate the design across grid sensing applications. The design has the added benefit of simplified implementation, increased scalability, and a reduction of component degradation over time.

GUID-20210407-CA0I-SZDM-SQSG-RJBVMFKRM0ZQ-low.gif Figure 2-2 Block Diagram of ADC-based BIM Design (ADS7128)