SLLSFC2D December   2020  – September 2021 ISO1642 , ISO1643 , ISO1644

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1  Absolute Maximum Ratings
    2. 6.2  ESD Ratings
    3. 6.3  Recommended Operating Conditions
    4. 6.4  Thermal Information
    5. 6.5  Power Ratings
    6. 6.6  Insulation Specifications
    7. 6.7  Safety-Related Certifications
    8. 6.8  Safety Limiting Values
    9. 6.9  Electrical Characteristics
    10. 6.10 Supply Current Characteristics
    11. 6.11 Timing Requirements
    12. 6.12 I2C Switching Characteristics
    13. 6.13 GPIO Switching Characteristics
    14. 6.14 Insulation Characteristics Curves
    15. 6.15 Typical Characteristics
  7. 7 Parameter Measurement Information
    1. 7.1 Parameter Measurement Information
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagrams
    3. 8.3 Isolation Technology Overview
    4. 8.4 Feature Description
      1. 8.4.1 Hot Swap
      2. 8.4.2 Protection Features
      3. 8.4.3 GPIO Channels
    5. 8.5 Isolator Functional Principle
      1. 8.5.1 Receive Direction (Left Diagram of Figure 1-1 )
      2. 8.5.2 Transmit Direction (Right Diagram of Figure 1-1 )
    6. 8.6 Device Functional Modes
  9. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 I2C Bus Overview
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
      3. 9.2.3 Application Curve
    3. 9.3 Insulation Lifetime
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
      1. 11.1.1 PCB Material
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Support Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

8.5 Isolator Functional Principle

To isolate a bidirectional signal path (SDA or SCL), the ISO1640 internally splits a bidirectional line into two unidirectional signal lines, each of which is isolated through a single-channel digital isolator. Each channel output is made open-drain to comply with the open-drain technology of I2C. Side 1 of the ISO1640 connects to a low-capacitance I2C node (up to 80 pF), while side 2 is designed for connecting to a fully loaded I2C bus with up to 400 pF of capacitance.

GUID-20200928-CA0I-FV5D-GHP4-14SVBBXMPS7P-low.gifFigure 8-4 SDA Channel Design and Voltage Levels at SDA1

At first sight, the arrangement of the internal buffers suggests a closed signal loop that is prone to latch-up. However, this loop is broken by implementing an output buffer (B) whose output low-level is raised by a diode drop to approximately 0.65 V, and the input buffer (C) that consists of a comparator with defined hysteresis. The comparator’s upper and lower input thresholds then distinguish between the proper low-potential of 0.4 V (maximum) driven directly by SDA1 and the buffered output low-level of B.

Figure 8-5 demonstrate the switching behavior of the I2C isolator, ISO164x, between a master node at SDA1 and a heavy loaded bus at SDA2.

GUID-20200930-CA0I-XNVG-N8FW-CQGKDW8GTKN4-low.gifFigure 8-5 SDA Channel Timing in Receive and Transmit Directions