SLLSET0D March   2016  – April 2021

PRODUCTION DATA

1. Features
2. Applications
3. Description
4. Revision History
5. Pin Configuration and Functions
6. Specifications
7. Parameter Measurement Information
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. Application Information Disclaimer
1. 9.1 Application Information
2. 9.2 Typical Applications
1. 9.2.1 Design Requirements
2. 9.2.2 Detailed Design Procedures
3. 9.2.3 Application Curves
10. 10Power Supply Recommendations
11. 11Device and Documentation Support
12. 12Mechanical, Packaging, and Orderable Information

• D|8
• DRB|8
• DRB|8

8.3.6 CAN Bus Short Circuit Current Limiting

The device has two protection features that limit the short circuit current when a CAN bus line is short-circuit fault condition: driver current limiting (both dominant and recessive states) and 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, thus the short circuit current may 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 ensure 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 their respective short circuit currents. The average short circuit current may be calculated with the following formula:

Equation 1. 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.