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

1.3 IEC 61557-8 Standard for Industrial Low-Voltage Distribution Systems

The purpose of this design is to offer an analog front-end for isolation barrier monitoring in unearthed industrial low-voltage distribution systems, such as DC fast-charging stations or solar string inverters. As per the safety standards, these systems include equipment for testing the isolation barrier compliant with the IEC 615578-8 standard. For more details on the IEC 615578-8 standard, see the IEC Webstore.

The circuit is designed to support IEC 615578-8:

  • Monitor the insulation resistance from DC lines to PE at regular intervals
  • Ground warning current is defined as 2 mA, which results in an isolation resistance of 500 Ω/V
  • Ground fault current is defined as 10 mA, which results in an isolation resistance of 100 Ω/V
  • Symmetrical and asymmetrical warning and fault detection
  • Isolation resistance monitoring accuracy < 15%
  • Measurement time < 10 s
  • Thermal stability (–5°C to +45°C)
  • Method proposed: switched-in resistive divider branch to determine isolation resistance of DC+, DC– vs PE
  • Test function: Report fault connections (to DC line or to PE)

This reference design offers additional advantages such as a reinforced isolated AFE with no external supply on the secondary. This allows the MCU to sit on the cold side and foster lower power consumption.