Design

Isolate CAN systems without compromising on performance

3rd December 2018
Alex Lynn

CAN interface has been a very popular serial communication standard in the industry due to its excellent prioritisation and arbitration capabilities. In systems with different voltage domains, isolation is typically used to protect the low voltage side from the high voltage side in case of any faults. 

Isolation also breaks any ground loops allowing only the desired signals to be transmitted, thereby improving signal quality. Isolated CAN is used for communication with the microcontroller in a wide range of applications such as solar inverters, circuit breakers, motor drives, PLC communication modules, telecom rectifiers, elevators, HVACs and EV charging infrastructures.

Isolated CAN can be broadly categorised into two types:

  • Basic isolation: In some applications like elevators and HVACs, CAN signalling is used between boards for communication and the CAN lines are not subjected to high voltage differences as a part of the normal operation. In such cases, basic isolated CAN would suffice from isolation perspective. Figure 1 shows an example of an elevator where the communication between the calling button operating panel and the communications board is achieved through isolated CAN. Figure 1. Isolated CAN in Elevators
  • Reinforced isolation: For solar inverter applications, the working voltage needs are higher and the electrical safety standard would have to be met by the isolator and hence reinforced isolation would be required. An example of isolated CAN used between the control module on the hot side and communication board of a computer or humanmachine interface (HMI) on the cold side is shown in.

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