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The common mode inductor is used in the CAN circuit, although it cannot be clearly improved in EMC. Many engineers will add circuits around the CAN. CAN chip has anti-static and transient voltage capability. Whether the common mode inductor should be added to the CAN Circuit is mainly considered from the aspect of electromagnetic compatibility

There are two open source circuits in the CAN, which can drive the bus to the dominant level, while the recessive level is realized through the discharge of the terminal resistor.

The inherent differential transmission of the bus has a good ability to suppress common-mode interference, The common mode interference from the outside can be well eliminated by subtracting two internal open source circuits. However, the two open source circuits are not ideal symmetry and are rising rapidly, which will lead to EMC electromagnetic compatibility problems.

We can see from the oscilloscope that the bus waveform is very standard, and the surge, static electricity, EFT transient pulse group and conducted immunity are normal. However, when conducting transmission test, it will show abnormalities. The bus that looks normal actually sends conducted interference outward.

In the CAN circuit, if you want to make the communication of the bus more reliable and solve the EMC problem of the interface, in addition to the CAN transceiver chip, another method is to add peripherals to the CAN interface. Common mode inductor is a good choice. Many CAN transceivers will exceed the conducted disturbance limit.

Common mode inductor can reduce disturbance, but bus plus common mode inductor may cause resonance and transient voltage problems. Common mode inductor will have parasitic inductance, resistance and other factors that will affect the quality of bus signal, leading to signal degradation. The common-mode inductor has a large inductance. When it is applied to the transceiver interface, hot plug and other working conditions, the two ends of the common-mode inductor generate transient high voltage, which may damage the CAN transceiver. Therefore, the resonance and transient voltage caused by it should still be considered in application.

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