SLLSF86C May   2018  – March 2022 ISOW1412 , ISOW1432

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Description Continued
  6. 6 Device Comparison Table
  7. 7 Pin Configuration and Functions
  8. 8 Specifications
    1. 8.1  Absolute Maximum Ratings
    2. 8.2  Recommended Operating Conditions
    3. 8.3  Thermal Information
    4. 8.4  Power Ratings
    5. 8.5  Insulation Specifications
    6. 8.6  Safety-Related Certifications
    7. 8.7  Safety Limiting Values
    8. 8.8  Electrical Characteristics
    9. 8.9  Supply Current Characteristics at VISOOUT = 3.3 V
    10. 8.10 Supply Current Characteristics at  VISOOUT = 5 V
    11. 8.11 Switching Characteristics at VISOOUT = 3.3 V
    12. 8.12 Switching Characteristics at VISOOUT = 5 V
    13. 8.13 Insulation Characteristics Curves
    14. 8.14 Typical Characteristics
  9. 9 Parameter Measurement Information
  10. 10Detailed Description
    1. 10.1 Overview
    2. 10.2 Power Isolation
    3. 10.3 Signal Isolation
    4. 10.4 RS-485
    5. 10.5 Functional Block Diagram
    6. 10.6 Feature Description
      1. 10.6.1 Power-Up and Power-Down Behavior
      2. 10.6.2 Protection Features
      3. 10.6.3 Failsafe Receiver
      4. 10.6.4 Glitch-Free Power Up and Power Down
    7. 10.7 Device Functional Modes
    8. 10.8 Device I/O Schematics
  11. 11Application and Implementation
    1. 11.1 Application Information
    2. 11.2 Typical Application
      1. 11.2.1 Design Requirements
      2. 11.2.2 Detailed Design Procedure
        1. 11.2.2.1 Data Rate, Bus Length and Bus Loading
        2. 11.2.2.2 Stub Length
        3. 11.2.2.3 Insulation Lifetime
  12. 12Power Supply Recommendations
  13. 13Layout
    1. 13.1 Layout Guidelines
    2. 13.2 Layout Example
  14. 14Device and Documentation Support
    1. 14.1 Documentation Support
      1. 14.1.1 Related Documentation
    2. 14.2 Receiving Notification of Documentation Updates
    3. 14.3 Support Resources
    4. 14.4 Trademarks
    5. 14.5 Electrostatic Discharge Caution
    6. 14.6 Glossary
  15. 15Mechanical, Packaging, and Orderable Information

11.2.2.1 Data Rate, Bus Length and Bus Loading

The RS-485 standard has typical curves similar to those shown in Figure 11-4. These curves show the inverse relationship between signaling rate and cable length. If the data rate of the payload between two nodes is lower, the cable length between the nodes can be longer. Use below Figure as a guideline for cable selection, data rate, cable length and subsequent jitter budgeting.

GUID-CDB9A9B3-FAB8-4C60-AF93-1D5E0DAE1421-low.gifFigure 11-4 Cable length vs Data rate characteristics

The current supplied by the driver must supply into a load because the output of the driver depends on this current. Add transceivers to the bus to increase the total bus loading. The RS-485 standard specifies a hypothetical term of a unit load (UL) to estimate the maximum number of possible bus loads. The UL represents a load impedance of approximately 12 kΩ. Standard-compliant drivers must be able to drive 32 of these ULs. The ISOW14x2 devices have 1/8 UL impedance transceiver and can connect up to 256 nodes to the bus.