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

10 What Factors Decide the Maximum Communication Distance in a CAN Network?

Several factors that impact maximum communication distance in a CAN network are:

  1. I*R drop of cable due to DC resistance will attenuate the signal as it reaches the farthest receiver. The minimum possible dominant signal at farthest receiver needs to be more than 900 mV (based on receiver threshold) for it to be recognized as valid dominant.
  2. As cable length is increased, capacitive load on the CAN bus increases which impacts dominant to recessive edge transition time which in turn is tied to minimum possible bit period (for example, maximum data rate).
  3. As explained in Section 8, during arbitration, a bit from the transmitter needs to reach the farthest receiver. So the maximum communication distance is closely dependent on the inverse of maximum data rate needed for end application. A conservative rule of thumb for bus lengths over 100 meters is derived from the product of the signaling rate in Mbps and the bus length in meters, which should be less than or equal to 50. Signaling Rate (Mbps) x Bus Length (m) <= 50