[Great God classroom] how to improve the CAN bus surge protection?

Although the CAN bus has strong anti-jamming capability, it will still be subject to static electricity and surge interference in practical applications. How can we improve the surge protection capability of the bus in the CAN bus network? In fact, it is not difficult, these devices make you worry-free.

First understand several typical transient disturbances.

Table 1 Comparison of several transient disturbances

From the table, it can be seen that the energy of the surge is the highest and the overcurrent is the greatest, so the danger is also the greatest. For surge protection, introduce the following three devices.

First, TVS

Figure 1 Bidirectional TVS tube characteristics

Reverse cut-off voltage VRWM: The highest voltage that TVS does not conduct;

Clamping voltage VC: the voltage across the diode when it conducts a certain current and increases with current;

Reverse current IR: reverse leakage current at VRWM voltage;

Breakdown voltage VBR: TVS tube through the specified test current IT (usually 1mA) voltage, said TVS tube conduction flag voltage;

Peak Current IPP: The maximum peak current of the 10/1000 μs or 8/20 μs wave that the TVS tube allows to pass through. Exceeding this current may cause permanent damage. Due to power limitations, the higher the breakdown voltage of the tube, the smaller the peak current allowed to pass;

CJ: The junction capacitance of the TVS tube is much larger than that of the ESD device. One-way is larger than the bidirectional one. The junction capacitance affects the response time of the TVS tube. When used in a communication bus, the bus bandwidth is limited.

Selection considerations parameters: VC, IPP, CJ

Second, the gas discharge tube

DC breakdown voltage VDC: when the voltage of 100V/s rising slope is applied to the discharge tube, the breakdown voltage of the discharge tube is caused. This is the nominal voltage of the discharge tube, and the dispersion of this parameter is large;

Pulse breakdown voltage VSI: The voltage at which the discharge tube breaks down when a voltage with a rising slope of 1 kV/μs is applied to the discharge tube. Impulse discharge current ID: divided into 8/20μs wave and 10/1000μs wave impulse discharge current.

Selection considerations: VDC, ID.

Two types of current wave test parameters are usually given in the device manuals such as TVS tubes and gas discharge tubes. 8/20μs wave and 10/1000μs wave, the main difference between the two is the duration and peak current, 8/20μs peak current is kA level, 10/1000μs peak current is A level. The durations are shown in Figure 2 and Figure 3, respectively.

Figure 2 8/20μs current wave

Figure 3 10/1000 μs current wave

Third, PTC resistance

Figure 4 PTC resistor characteristics

Maximum operating voltage VMAX: The maximum voltage that the PTC resistor can sustain at the maximum allowable temperature;

Hold current Ihold: the PTC resistance is stable at the operating point resistance;

Trigger current Itrip: The minimum current that can cause the resistance to increase in steps;

Rated zero power resistor Rn: initial resistance of PTC at normal temperature;

Switching temperature TC: The resistance shows a step increase in temperature, and the resistance is 2 times the minimum resistance.

Selection considerations: Rn, Itrip, Ihold.

Fourth, anti-surge integration program

Figure 5 Surge test circuit

Figure 6 EMC performance of CTM1051(A)HP

Figure 7 Application schematic

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