SLLSF09F December   2017  – August 2026 ISO1042

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
    3. 5.3  Transient Immunity
    4. 5.4  Recommended Operating Conditions
    5. 5.5  Thermal Information
    6. 5.6  Power Ratings
    7. 5.7  Insulation Specifications
    8. 5.8  Safety-Related Certifications
    9. 5.9  Safety Limiting Values
    10. 5.10 Electrical Characteristics - DC Specification
    11. 5.11 Switching Characteristics
    12. 5.12 Insulation Characteristics Curves
    13. 5.13 Typical Characteristics
  7. 6 Parameter Measurement Information
    1. 6.1 Test Circuits
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 CAN Bus States
      2. 7.3.2 Digital Inputs and Outputs: TXD (Input) and RXD (Output)
      3. 7.3.3 Protection Features
        1. 7.3.3.1 TXD Dominant Timeout (DTO)
        2. 7.3.3.2 Thermal Shutdown (TSD)
        3. 7.3.3.3 Undervoltage Lockout and Default State
        4. 7.3.3.4 Floating Pins
        5. 7.3.3.5 Unpowered Device
        6. 7.3.3.6 CAN Bus Short Circuit Current Limiting
    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
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Bus Loading, Length and Number of Nodes
        2. 8.2.2.2 CAN Termination
      3. 8.2.3 Application Curve
        1. 8.2.3.1 Insulation Lifetime
    3. 8.3 DeviceNet Application
    4. 8.4 Power Supply Recommendations
    5. 8.5 Layout
      1. 8.5.1 Layout Guidelines
        1. 8.5.1.1 PCB Material
      2. 8.5.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Documentation Support
      1. 9.1.1 Related Documentation
    2. 9.2 Receiving Notification of Documentation Updates
    3. 9.3 Support Resources
    4. 9.4 Trademarks
    5. 9.5 Electrostatic Discharge Caution
    6. 9.6 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

7.3.3.6 CAN Bus Short Circuit Current Limiting

The device has two protection features that limit the short circuit current when a CAN bus line has a short-circuit fault condition. The first protection feature is driver current limiting (both dominant and recessive states) and the second feature is TXD dominant state time out to prevent permanent higher short circuit current of the dominant state during a system fault. During CAN communication the bus switches between dominant and recessive states, therefore the short circuit current can be viewed either as the instantaneous current during each bus state or as an average current of the two states. For system current (power supply) and power considerations in the termination resistors and common-mode choke ratings, use the average short circuit current. Determine the ratio of dominant and recessive bits by the data in the CAN frame plus the following factors of the protocol and PHY that force either recessive or dominant at certain times:

  • Control fields with set bits
  • Bit stuffing
  • Interframe space
  • TXD dominant time out (fault case limiting)

These factors verify a minimum recessive amount of time on the bus even if the data field contains a high percentage of dominant bits. The short circuit current of the bus depends on the ratio of recessive to dominant bits and the respective short circuit currents. Use Equation 2 to calculate the average short circuit current.

Equation 2. IOS(AVG) = %Transmit × [(%REC_Bits × IOS(SS)_REC) + (%DOM_Bits × IOS(SS)_DOM)] + [%Receive × IOS(SS)_REC]

where

  • IOS(AVG) is the average short circuit current
  • %Transmit is the percentage the node is transmitting CAN messages
  • %Receive is the percentage the node is receiving CAN messages
  • %REC_Bits is the percentage of recessive bits in the transmitted CAN messages
  • %DOM_Bits is the percentage of dominant bits in the transmitted CAN messages
  • IOS(SS)_REC is the recessive steady state short circuit current
  • IOS(SS)_DOM is the dominant steady state short circuit current
Note:

Consider the short circuit current and possible fault cases of the network when sizing the power ratings of the termination resistance and other network components.