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

 

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  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

5 What’s the Difference Between Common Mode Range and Bus Standoff Mentioned in Data Sheet?

The CAN standard ISO11898-2(2016) defines common mode voltage range as the range of common mode voltage present on CAN bus lines for which a CAN receiver is able to faithfully recover differential signals on the bus and replicate them on RXD. ISO1044 and ISOW1044 have ±12 V common mode voltage range, whereas ISO1042 has ±30 V, both mentioned in valid operating conditions. This voltage range is with respect to bus side ground, for example, GND2. Bus standoff, also known as bus short circuit voltage or bus fault protection, is specified in the absolute maximum ratings table. For ISO1042, it is ±70 V whereas for ISO1044 and ISOW1044 it is ±58 V. This means under temporary fault conditions of say 12-V/24-V/48-V supply voltage shorting to the CAN bus, both devices will withstand that short condition and not get damaged.