SLLSF22H April   2018  β€“ June 2024 ISO1410 , ISO1412 , ISO1430 , ISO1432 , ISO1450 , ISO1452

PRODUCTION DATA  

  1.   1
  2. Features
  3. Applications
  4. Description
  5. Description Continued
  6. Device Comparison Table
  7. Pin Configuration and Functions
    1.     Pin Functions: Full-Duplex Device
    2.     Pin Functions: Half-Duplex Device
  8. Specifications
    1. 7.1  Absolute Maximum Ratings
    2. 7.2  ESD Ratings
    3. 7.3  Recommended Operating Conditions
    4. 7.4  Thermal Information
    5. 7.5  Power Ratings
    6. 7.6  Insulation Specifications
    7. 7.7  Safety-Related Certifications
    8. 7.8  Safety Limiting Values
    9. 7.9  Electrical Characteristics: Driver
    10. 7.10 Electrical Characteristics: Receiver
    11. 7.11 Supply Current Characteristics: Side 1 (ICC1)
    12. 7.12 Supply Current Characteristics: Side 2 (ICC2)
    13. 7.13 Switching Characteristics: Driver
    14. 7.14 Switching Characteristics: Receiver
    15. 7.15 Insulation Characteristics Curves
    16. 7.16 Typical Characteristics
  9. Parameter Measurement Information
  10. Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Electromagnetic Compatibility (EMC) Considerations
      2. 9.3.2 Failsafe Receiver
      3. 9.3.3 Thermal Shutdown
      4. 9.3.4 Glitch-Free Power Up and Power Down
    4. 9.4 Device Functional Modes
      1. 9.4.1 Device I/O Schematics
  11. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
        1. 10.2.2.1 Data Rate and Bus Length
        2. 10.2.2.2 Stub Length
        3. 10.2.2.3 Bus Loading
      3. 10.2.3 Application Curves
        1. 10.2.3.1 Insulation Lifetime
  12. 11Power Supply Recommendations
  13. 12Layout
    1. 12.1 Layout Guidelines
      1. 12.1.1 PCB Material
    2. 12.2 Layout Example
  14. 13Device and Documentation Support
    1. 13.1 Documentation Support
      1. 13.1.1 Related Documentation
        1. 13.1.1.1 Related Links
    2. 13.2 Receiving Notification of Documentation Updates
    3. 13.3 Support Resources
    4. 13.4 Trademarks
    5. 13.5 Electrostatic Discharge Caution
    6. 13.6 Glossary
  15. 14Revision History
  16. 15Mechanical, Packaging, and Orderable Information

Failsafe Receiver

The differential receiver of the ISO14xx devices has failsafe protection from invalid bus states caused by:

  • Open bus conditions such as a broken cable or a disconnected connector
  • Shorted bus conditions such as insulation breakdown of a cable that shorts the twisted-pair
  • Idle bus conditions that occur when no driver on the bus is actively driving

The differential input of the RS-485 receiver is 0 in any of these conditions for a terminated transmission line. The receiver outputs a failsafe logic-high state so that the output of the receiver is not indeterminate.

The receiver thresholds are offset in the receiver failsafe protection so that the indeterminate range of the does not include a 0 V differential. The receiver output must generate a logic high when the differential input (VID) is greater than 200 mV to comply with the RS-485 standard. The receiver output must also generate a output a logic low when VID is less than –200 mV to comply with the RS-485 standard. The receiver parameters that determine the failsafe performance are VTH+, VTH–, and VHYS. Differential signals less than –200 mV always cause a low receiver output as shown in the Electrical Characteristics table. Differential signals greater than 200 mV always cause a high receiver output. A differential input signal that is near zero is still greater than the VTH+ threshold which makes the receiver output logic high. The receiver output goes to a low state only when the differential input decreases by VHYS to less than VTH+.

The internal failsafe biasing feature removes the need for the two external resistors that are typically required with traditional isolated RS-485 transceivers as shown in Figure 9-3.

ISO1450 ISO1452 ISO1410 ISO1412 ISO1430 ISO1432 Failsafe TransceiverFigure 9-3 Failsafe Transceiver