Murata Auto LANs Suppression of Noise in CANs Using CMCCs

Suppression of Noise in CANs

Problems of Electromagnetic Noise in CANs and Noise Suppression Components
In CANs, the quality of communication demands reliability, and electromagnetic noise, in particular, has an adverse effect on reliability. To resolve the issues of electromagnetic noise, it is necessary to suppress the generation of the noise so it will not adversely affect the wireless communication, etc. used inside automobiles. High noise-resistance properties must also be ensured in order to maintain communication quality even as surrounding noise seeps in. For example, in terms of radiated noise, harmonic noise with a signal frequency of 250kHz (or 500kHz) is radiated at high levels up to frequency bands of several dozen megahertz.

For its part, Murata offers the DLW43SH series of common mode choke coils to suppress the noise in CANs.

Noise Suppression Results Achieved by DLW Chokes and Evaluation of Effects on Waveforms
In order to verify the effects achieved by the DLW43SH series in CANs, Murata evaluated the radiated noise using a CAN evaluation board. It also performed BCI tests and waveform evaluations.

Evaluation Results

Radiated Noise Evaluation
Murata verified a noise-suppression effect was achieved by adding the DLW43SH series. For 250kHz pulses, the noise suppression effect is approximately 25dB at a 20.5MHz vertical polarized wave frequency. For 500kHz pulses, it is approximately 18dB at a 21.0MHz vertical polarized wave frequency.

BCI Tests
With the DLW43SH series placed in the circuit, malfunctioning was suppressed, and 100 mA was cleared at all frequencies (1MHz to 400MHz).

Waveform Evaluation
With the DLW43SH series placed in the circuit, hardly any effect on the waveforms was found compared to cases where short-circuiting was present.

Evaluation Environment

Measurement Conditions
The star topology (Figure 1, below) was used to evaluate the radiated noise. On the CAN evaluation board, 250kHz and 500kHz pulses were input from the clock oscillator to the Txd terminal of the transceiver made by company A to generate the CAN signals. Open terminations were used for the nodes at the reception to simulate high-impedance ICs.

Results at 250kHz Pulses

A noise-suppression effect was achieved by adding the DLW43SH510XK2. (Noise was reduced by 25.1dB at a 20.5MHz vertical polarized wave frequency.)

Results at 500kHz pulses

By adding the DLW43SH510XK2, a noise-suppression effect was achieved. (Noise was reduced by 17.8dB at a 21.0MHz vertical polarized wave frequency.)

Radiated Noise Evaluation Summary

250kHz Pulses
When no filter was used, a high level of noise was found from 150kHz to 30MHz. By adding a choke coil from Murata's DLW43SH series, a noise-suppression effect was achieved. The DLW43SH series achieved a noise-suppression effect of approximately 26dB at a 20.5MHz vertical polarized wave frequency.

500kHz Pulses
When no filter was used, a high level of noise was found from 150kHz to 30MHz. By adding a choke coil from Murata's DLW43SH series, a noise-suppression effect was achieved. A noise-suppression effect of approximately 18dB at a 21.0MHz vertical polarized wave frequency was achieved.

Results of BCI Test

Malfunctioning was suppressed by adding choke coils from the DLW43SH series. 100mA was cleared at all frequencies (1MHz to 400MHz).

BCI Test Results Summary

When no filter was used, malfunctioning occurred at frequencies from 4MHz to 15MHz, but when common mode choke coils were added, the malfunctioning was suppressed. With the DLW43SH series, malfunctioning was suppressed, and 100mA was cleared at all frequencies (1MHz to 400MHz).

Waveform Evaluation - Measurement Conditions

The star topology (Figure 2, below) was used to conduct the waveform evaluation. On the CAN evaluation board, 500kHz pulses were input from the function generator to the Txd terminal of the transceiver made by company A to generate the CAN signals. Open terminations were used for the nodes at the reception to simulate high-impedance ICs. As the waveforms, differential voltage Vd between CAN_H and CAN_L after transit through the filter was measured.

Waveform Evaluation Results Summary

Compared to when no filter was used, hardly any effect on the waveforms was found with the DLW43SH series.

Overall Results Summary

Radiated Noise Evaluation
By adding the DLW43SH series, it was verified that a noise-suppression effect was achieved. For 250 kHz pulses, the noise-suppression effect is approximately 25dB at a 20.5MHz vertical polarized wave frequency. For 500kHz pulses, it is approximately 18dB at a 21.0MHz vertical polarized wave frequency.

BCI Tests
With the DLW43SH series, malfunctioning was suppressed, and 100mA was cleared at all frequencies (1MHz to 400MHz).

Waveform Evaluation
With the DLW43SH series, hardly any effect on the waveforms was found compared with cases of short-circuiting.

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