SLLSF17C August   2019  – October 2024 TCAN1044-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
    3. 5.3  ESD Ratings
    4. 5.4  Recommended Operating Conditions
    5. 5.5  Thermal Characteristics
    6. 5.6  Supply Characteristics
    7. 5.7  Dissipation Ratings
    8. 5.8  Electrical Characteristics
    9. 5.9  Switching Characteristics
    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 Pin Description
        1. 7.3.1.1 TXD
        2. 7.3.1.2 GND
        3. 7.3.1.3 VCC
        4. 7.3.1.4 RXD
        5. 7.3.1.5 VIO
        6. 7.3.1.6 CANH and CANL
        7. 7.3.1.7 STB (Standby)
      2. 7.3.2 CAN Bus States
      3. 7.3.3 TXD Dominant Timeout (DTO)
      4. 7.3.4 CAN Bus Short Circuit Current Limiting
      5. 7.3.5 Thermal Shutdown (TSD)
      6. 7.3.6 Undervoltage Lockout
      7. 7.3.7 Unpowered Device
      8. 7.3.8 Floating pins
    4. 7.4 Device Functional Modes
      1. 7.4.1 Operating Modes
      2. 7.4.2 Normal Mode
      3. 7.4.3 Standby Mode
        1. 7.4.3.1 Remote Wake Request via Wake-Up Pattern (WUP) in Standby Mode
      4. 7.4.4 Driver and Receiver Function
  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 CAN Termination
      2. 8.2.2 Detailed Design Procedures
        1. 8.2.2.1 Bus Loading, Length and Number of Nodes
      3. 8.2.3 Application Curves
    3. 8.3 System Examples
    4. 8.4 Power Supply Recommendations
    5. 8.5 Layout
      1. 8.5.1 Layout Guidelines
      2. 8.5.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Receiving Notification of Documentation Updates
    2. 9.2 Support Resources
    3. 9.3 Trademarks
    4. 9.4 Electrostatic Discharge Caution
    5. 9.5 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information

Package Options

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

7.3.4 CAN Bus Short Circuit Current Limiting

The TCAN1044-Q1 has several protection features that limit the short circuit current when a CAN bus line is shorted. These include CAN driver current limiting in the dominant and recessive states and TXD dominant state timeout which prevents permanently having the higher short circuit current of a dominant state in case of a system fault. During CAN communication the bus switches between the dominant and recessive states, thus the short circuit current may be viewed as either the current during each bus state or as a DC average current. When selecting termination resistors or a common mode choke for the CAN design the average power rating, IOS(AVG), should be used. The percentage dominant is limited by the TXD DTO and the CAN protocol which has forced state changes and recessive bits due to bit stuffing, control fields, and interframe space. These ensure there is a minimum amount of recessive time on the bus even if the data field contains a high percentage of dominant bits.

The average 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 using 2.

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

This short circuit current and the possible fault cases of the network should be taken into consideration when sizing the power supply used to generate the transceivers VCC supply.