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

6 Now That I Have Taken Care of the Termination Resistor, What Other Components do I Need on the Bus Side?

ISO1042, ISO1044, and ISOW1044 have integrated ±8 kV IEC ESD protection (per 61000-4-2) on the bus side, which is tested with no other components present on the bus. Sometimes, system designers use common-mode-chokes (CMCs) to reduce Emissions to meet requirements such as CISPR32, or to improve Immunity performance to meet Electrical Fast Transients per IEC61000-4-4. The CMC attenuates the common mode signal going into the device or coming out of it. Split termination capacitor may also help in noisy-system scenarios-this again helps in emissions reduction or immunity improvement.

A low value series resistors (~10 ohm) can be used on both CANH/CANL lines in case lightning surges (tested per IEC61000-4-5) are expected on the cable to reduce the current that flows to internal clamping structures of the device during surge events. These series resistor will attenuate differential signal as it forms a divider with the 60 ohm loading on the bus. Final components on the bus are very system specific and the end equipment should be tested to fully confirm which components are needed in the its design. Please refer to the TI design Isolated CAN Module With Integrated Power Reference Design that implements these design considerations and shows practical lab-tested results.