SLLA486B May   2020  – October 2024 ISO1042 , ISO1042-Q1 , ISO1044 , ISO1050 , ISOW1044

 

  1.   1
  2.   Top Design Questions About Isolated CAN Bus Design
  3.   Trademarks
  4. 1 When Do I Need to Isolate CAN?
  5. 2 What are the Options Available to Isolate CAN Bus?
  6. 3 Now That I Have Isolated CAN Signal Path, How Do I Generate Isolated Power?
  7. 4 What’s the Reason Behind Terminating the Bus, Do I Need it, and How to Achieve it?
  8. 5 What’s the Difference Between Common Mode Range and Bus Standoff Mentioned in Data Sheet?
  9. 6 Now That I Have Taken Care of the Termination Resistor, What Other Components do I Need on the Bus Side?
  10. 7 When Connecting Isolated CAN Nodes in a Network, What Should be Done with the Floating Bus-Side Ground Connection?
  11. 8 Is There a Limitation on Minimum Data Rate That I Can Operate? What About the Maximum Data Rate Achievable in a Network?
  12. 9 Is There a Limit on Maximum Number of Nodes That I Can Connect in CAN Network?
  13. 10What Factors Decide the Maximum Communication Distance in a CAN Network?
  14. 11What is the Maximum Value of Bus Capacitance That Can be Introduced Between CANH to GND and CANL to GND? Can Higher Capacitance Damage the Device?
  15. 12Is There a Way to Extend the Maximum Communication Distance?
  16. 13What is Stub Length? What are the Design Considerations Around it?
  17. 14I am Seeing Larger Differential CAN Voltage for Some Bits of CAN Packet Compared to Rest of the Packet When I am Communicating in a Network with Multiple Nodes Connected. Why?
  18. 15References
  19. 16Revision History

1 When Do I Need to Isolate CAN?

The CAN standard ISO11898-2(2016) requires ±12 V common mode voltage range support for a compliant CAN transceiver. This means a CAN receiver needs to tolerate up to ±12 V common mode voltage on CAN lines with respect to bus-side ground and still be able to faithfully replicate differential voltage transitions on the bus. There are CAN transceivers available from TI, such as TCAN1042, which support an extended common mode range of up to ±30 V. When the communicating nodes in a CAN network have larger ground potential differences (GPDs), which are higher than the supported common mode voltage range of the transceiver, due to longer communication distance or system ground being noisy (such as in motor drive applications), isolating the CAN node becomes necessary. The isolation barrier also acts as high impedance to common mode noise transients (such as ESD/EFT/Surge) that are common in industrial environments. Proper design in some application scenarios can enable system designers to drop all common mode noise across the isolation barrier, thereby eliminating some external components commonly seen on CAN bus. For more details, please refer to: How to use isolation to improve ESD, EFT and surge immunity in industrial systems.