SLLS612F June   2004  – February 2023 SN65HVD485E

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison Table
    1.     6
  6. 6 Pin Configuration and Functions
  7. 7 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  Electrical Characteristics: Driver
    6. 7.6  Electrical Characteristics: Receiver
    7. 7.7  Power Dissipation Characteristics
    8. 7.8  Supply Current
    9. 7.9  Switching Characteristics: Driver
    10. 7.10 Switching Characteristics: Receiver
    11. 7.11 Dissipation Ratings
    12. 7.12 Typical Characteristics
      1.      Parameter Measurement Information
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
    4. 8.4 Device Functional Modes
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
        1. 9.2.1.1 Data Rate and Bus Length
        2. 9.2.1.2 Stub Length
        3. 9.2.1.3 Bus Loading
        4. 9.2.1.4 Receiver Failsafe
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Power Usage in an RS-485 Transceiver
      3. 9.2.3 Application Curve
    3. 9.3 Power Supply Recommendations
    4. 9.4 Layout
      1. 9.4.1 Layout Guidelines
      2. 9.4.2 Layout Example
  10. 10Device and Documentation Support
    1. 10.1 Device Support
      1. 10.1.1 Device Nomenclature
        1. 10.1.1.1 Thermal Characteristics of IC Packages
    2. 10.2 Documentation Support
      1. 10.2.1 Related Documentation
    3. 10.3 Support Resources
    4. 10.4 Trademarks
    5. 10.5 Electrostatic Discharge Caution
    6. 10.6 Glossary
  11. 11Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

9.2.1.4 Receiver Failsafe

The differential receiver of the SN65HVD485E device is failsafe to invalid bus states caused by the following:

  • Open bus conditions such as a disconnected connector
  • Shorted bus conditions such as cable damage shorting the twisted pair together
  • Idle bus conditions that occur when no driver on the bus is actively driving

In any of these cases, the differential receiver outputs a failsafe logic-high state so that the output of the receiver is not indeterminate.

Receiver failsafe is accomplished by offsetting the receiver thresholds such that the input indeterminate range does not include zero volts differential. To comply with the RS-422 and RS-485 standards, the receiver output must output a high when the differential input VID is more positive than 200 mV, and it must output a Low when VID is more negative than –200 mV. The receiver parameters that determine the failsafe performance are VIT+, VIT–, and Vhys (the separation between VIT+ and VIT–). As shown in the Section 7.6 table, differential signals more negative than –200 mV cause a low receiver output, and differential signals more positive than 200 mV cause a high receiver output.

When the differential input signal is close to zero, it is still above the VIT+ threshold, and the receiver output is High. Only when the differential input is more than Vhys below VIT+ does the receiver output transition to a Low state. Therefore, the noise immunity of the receiver inputs during bus fault conditions includes the receiver hysteresis value (Vhys) as well as the value of VIT+.