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

Resistive Bridge

As Section 1 explained, isolation and a high-voltage bus monitoring circuit is implemented in the schematics and printed-circuit board (PCB). Hardware that measures isolation resistance and leakage current is built with a temporary isolation breaking circuit.

As Figure 2-6 shows, thin film resistors R3, R4, R5, R6, R7, R9, R10, R11, R12, and R13 are used as a potential divider network switched in the high-voltage positive line, whereas R29, R30, R31, R32, R28, R22, R23, R24, R25, and R20 are switched in the high-voltage negative line. Thin film resistors are chosen to have less tolerance, high reliability, and a low temperature coefficient of resistance (TCR). Any deviation in resistor values has an impact on the error of interlock leakage current and isolation resistance calculations.

GUID-20220401-SS0I-TBVK-FRTS-FK3W29TLPKB8-low.pngFigure 2-6 Schematic High-Voltage Resistive Bridge

DC fast chargers supply power to the 400-V battery management system bypassing the onboard battery charger. Conversely, in string inverters, DC lines coming from the PV string panels go up to 1 kV. The current allowed through the resistive bridge determines the delay time in the isolated voltage. Further details are found in Section 1.2.