SLLS983L June   2009  – October 2023 ISO1050

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Revision History
  6. 5 Pin Configuration and Functions
  7. 6 Specifications
    1. 6.1  Absolute Maximum Ratings
    2. 6.2  ESD Ratings
    3. 6.3  Recommended Operating Conditions
    4. 6.4  Thermal Information
    5. 6.5  Power Ratings
    6. 6.6  Insulation Specifications
    7. 6.7  Safety-Related Certifications
    8. 6.8  Safety Limiting Values
    9. 6.9  Electrical Characteristics - DC Specification
    10. 6.10 Switching Characteristics
    11. 6.11 Insulation Characteristics Curves
    12. 6.12 Typical Characteristics
  8. 7 Parameter Measurement Information
  9. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 CAN Bus States
      2. 8.3.2 Digital Inputs and Outputs
      3. 8.3.3 Protection Features
        1. 8.3.3.1 TXD Dominant Time-Out (DTO)
        2. 8.3.3.2 Thermal Shutdown
        3. 8.3.3.3 Undervoltage Lockout and Fail-Safe
        4. 8.3.3.4 Floating Pins
        5. 8.3.3.5 CAN Bus Short-Circuit Current Limiting
    4. 8.4 Device Functional Modes
  10. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Bus Loading, Length and Number of Nodes
        2. 9.2.2.2 CAN Termination
      3. 9.2.3 Application Curve
  11. 10Power Supply Recommendations
    1. 10.1 General Recommendations
    2. 10.2 Power Supply Discharging
  12. 11Layout
    1. 11.1 Layout Guidelines
      1. 11.1.1 PCB Material
    2. 11.2 Layout Example
  13. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Support Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  14. 13Mechanical, Packaging, and Orderable Information

8.3.3.5 CAN Bus Short-Circuit Current Limiting

The device has several protection features that limit the short-circuit current when a CAN bus line is shorted. These include driver current limiting (dominant and recessive). The device has 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 with the data and control fields bits, thus the short-circuit current may be viewed either as the instantaneous current during each bus state, or as a DC average current. 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 ensure a minimum recessive amount of time on the bus even if the data field contains a high percentage of dominant bits.

Note:

The short-circuit current of the bus depends on the ratio of recessive to dominant bits and their respective short-circuit currents. The average short-circuit current may be calculated with the following formula:

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.