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

2.3.2.1 Differential to Single-Ended Conversion

As stated, the isolation voltage is monitored with an AMC3330 across the isolation barrier. The output of the AMC3330 is a fully-differential analog signal comprised of the OUTP and OUTN pins centered around a common-mode voltage of 1.44 V that can be fed directly to a stand-alone analog-to-digital converter (ADC).


GUID-484203D6-9550-4A3D-8E2E-3F7395D0A141-low.gif

Figure 2-9 AMC3330 Output Behavior

The MSP430 and C2000 family of processors have embedded single-ended input ADCs. The addition of a differential to single-ended amplifier output stage, illustrated in Figure 2-10, allows the full output range of the AMC3330 to be converted to the 3.3-V range which is designed for the single-ended embedded ADC. The signal range is amplified, and the common-mode voltage is set to half of the ADC range using 1.65 V provided by REF2033.


GUID-20210809-SS0I-BCG8-BGCG-SQHWCQDGKM35-low.svg

Figure 2-10 Differential to Single-Ended Conversion – Output AMC3330

If R1 = R4 and R2 = R3 Equation 19 describes the behavior of the differential-to-single-ended conversion.

Equation 19. V out = V outP × R 4 R 3 - V outN × R 1 R 2 + V ref

The TLV6001 operational amplifier for cost-sensitive systems is used for this purpose. Further details on the TI isolated amplifier family differential output conversion to singled ended are found in the Interfacing a Differential-Output (Isolated) Amplifier to a Single-Ended Input ADC application brief.

The AMC3330 has a maximum output voltage swing of ±2 V. This has to be translated to a single-ended signal between 0 V and 3.3 V. Hence, a gain of 0.825 is set with the ratio of R1/R2 and R4/R3. The common-mode voltage of 1.65 V is set with the Vref / 2 output of the REF2033 voltage reference.