TIDUEZ8C december   2022  – june 2023

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1. 1.1 Insulation Monitoring
    2. 1.2 Impact of Parasitic Isolation Capacitance
    3. 1.3 IEC 61557-8 Standard for Industrial Low-Voltage Distribution Systems
    4. 1.4 Key System Specifications
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Highlighted Products
      1. 2.2.1 TPSI2140
      2. 2.2.2 AMC3330
      3. 2.2.3 TPS7A24
      4. 2.2.4 REF2033
      5. 2.2.5 TLV6001
    3. 2.3 Design Considerations
      1. 2.3.1 Resistive Bridge
      2. 2.3.2 Isolated Analog Signal Chain
        1. 2.3.2.1 Differential to Single-Ended Conversion
        2. 2.3.2.2 High-Voltage Measurement
        3. 2.3.2.3 Signal Chain Error Analysis
      3. 2.3.3 Loss of PE Detection
      4. 2.3.4 Insulation Monitoring on AC Lines
      5. 2.3.5 PCB Layout Recommendations
  9. 3Hardware, Software, Testing Requirements, and Test Results
    1. 3.1 Hardware Requirements
      1. 3.1.1 Connectors
      2. 3.1.2 Default Jumper Configuration
      3. 3.1.3 Prerequisites
    2. 3.2 Software Requirements
    3. 3.3 Software
    4. 3.4 Test Setup
    5. 3.5 Test Results
  10. 4Design and Documentation Support
    1. 4.1 Design Files
      1. 4.1.1 Schematics
      2. 4.1.2 BOM
    2. 4.2 Documentation Support
    3. 4.3 Support Resources
    4. 4.4 Trademarks
  11. 5About the Author
  12. 6Revision History

2.3.2.3 Signal Chain Error Analysis

The conditioning can be done through the calculation tool Isolated Amplifier Voltage Sensing Excel Calculator. The tool offers a detailed worst-case error analysis across temperature considering gain error and drift, and offset error and drift, and non-linearity drift. Note that the error analysis is output referenced.

The main sources of error in the signal chain are the resistor tolerances, gain and offset errors off the AMC3330, and gain and offset errors in the differential-to-single-ended conversion circuitry. There is another TIDA-010232 specific worst-case error calculation excel sheet available on the reference design page. This sheet assumes the absolute worst-case for each parameter in the signal chain and finds the combination of these which results in the worst accuracy. As shown in Section 3.5, the actual measured accuracy is in most cases better than the worst-case assumption.

If higher accuracy is desired, precision op amps can be used for the differential-to-single-ended conversion, such as the TLV6001 pin-to-pin compatible OPA320 (Voffset 0.15 mV). To improve accuracy even further, the differential-to single-ended conversion can be removed by choosing a dedicated differential input ADC instead of the internal ADC of the C2000 microcontroller.