TIDUEZ8 May   2021

 

  1.   Description
  2.   Resources
  3.   Features
  4.   Applications
  5.   5
  6. 1System Description
    1. 1.1 Insulation Monitoring
    2. 1.2 Isolation Capacitance
    3. 1.3 IEC 61557-8 Standard for Industrial Low-Voltage Distribution Systems
    4. 1.4 Key System Specifications
  7. 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 PCB Layout Recommendations
  8. 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 Test Setup
    4. 3.4 Test Results
  9. 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
  10. 5About the Authors

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

The purpose of this design is to offer an analog front-end solution 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 should 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.

This analog front end was designed to support IEC 615578-8 requirements:

  • Monitor the insulation resistance from DC lines to PE at regular intervals
  • Ground warning current is defined as 20 mA which results in an isolation resistance of 200 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% as per standard
  • Isolation monitoring should indicate resistance and maximum capacitance to earth range
  • Measurement time < 10 s as per standard
  • Thermal stability (–5°C to +45°C)
  • Method proposed: switch 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 analog front end with no external supply on the secondary. This allows the MCU to sit on the cold side and foster lower power consumption.