SLLSE49E September   2010  – October 2024 SN65HVD1780-Q1 , SN65HVD1781-Q1 , SN65HVD1782-Q1

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1  Absolute Maximum Ratings
    2. 5.2  ESD Ratings—AEC
    3. 5.3  ESD Ratings—IEC
    4. 5.4  Recommended Operating Conditions
    5. 5.5  Thermal Information
    6. 5.6  Electrical Characteristics
    7. 5.7  Power Dissipation Ratings
    8. 5.8  Switching Characteristics
    9. 5.9  Package Dissipation Ratings
    10. 5.10 Typical Characteristics
  7. 6 Parameter Measurement Information
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Bus Fault Conditions
      2. 7.3.2 Receiver Failsafe
      3. 7.3.3 Hot-Plugging
    4. 7.4 Device Functional Modes
  9. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
        1. 8.2.1.1 Data Rate and Bus Length
        2. 8.2.1.2 Bus Loading
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Stub Length
        2. 8.2.2.2 Receiver Failsafe
      3. 8.2.3 Application Curve
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Device Support
      1. 9.1.1 Third-Party Products Disclaimer
    2. 9.2 Documentation Support
      1. 9.2.1 Related Documentation
    3. 9.3 Receiving Notification of Documentation Updates
    4. 9.4 Support Resources
    5. 9.5 Trademarks
    6. 9.6 Electrostatic Discharge Caution
    7. 9.7 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

8.2.2.2 Receiver Failsafe

The differential receivers of the SN65HVD178x-Q1 family have receiver input thresholds that are offset, so the receiver output state is known for the following three fault conditions:

  • 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 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 200mV, and must output a Low when VID is more negative than –200mV. The receiver parameters which determine the failsafe performance are VIT(+), VIT(–), and VHYS (the separation between VIT(+) and VIT(–)). As shown in the Electrical Characteristics table, differential signals more negative than –200mV always cause a Low receiver output, and differential signals more positive than 200mV always cause a High receiver output.

When the differential input signal is close to zero, the signal is still above the maximum VIT(+) threshold of –35 mV, 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 a bus fault condition includes the receiver hysteresis value, VHYS, as well as the value of VIT(+).

SN65HVD1780-Q1 SN65HVD1781-Q1 SN65HVD1782-Q1 Noise Immunity Under Bus Fault ConditionsFigure 8-5 Noise Immunity Under Bus Fault Conditions