In modern electronic systems, CAN Bus (Controller Area Network Bus) is a commonly used communication protocol, and standard CAN usually refers to CAN 2.0A and CAN 2.0B protocols, with a maximum communication rate of 1Mbps. High speed CAN usually refers to the CAN FD (CAN Flexible Data rate) protocol. As we all know, there may be a threat of electrostatic discharge (ESD EOS) in the working environment. Therefore, engineers place ESD diodes in CAN BUS circuits for electrostatic surge protection. However, ICs may also be damaged by electrostatic surges, causing them to malfunction. What is the reason for this?

1、 Why is the back end of the ESD diode still damaged when placed? Reason

Based on his years of experience in ESD device selection and rectification, Shanghai Leimao EMC has analyzed the following:

1. Excessive surge energy of electrostatic discharge: If the energy of electrostatic discharge exceeds the capacity of the anti-static diode, some energy may still be conducted to the device, causing it to burn out. So the surge resistance of each ESD device is different, try to reproduce the surge level as much as possible, and evaluate and select suitable devices.

2. The clamping voltage VC is too high, exceeding the voltage range that the backend IC can withstand, resulting in damage. This situation is very common.

3. Wiring or grounding issues: Improper wiring of the CAN bus, such as excessively long lines, routing too close to interference sources, or poor grounding, may result in static electricity not being able to be effectively discharged through diodes in a timely manner, causing damage to the devices.

The above three situations are quite common.

Therefore, it is crucial to choose appropriate electrostatic protection devices. Correctly selecting CAN Bus electrostatic protection devices can not only ensure the stable operation of the system, but also effectively extend the service life of the equipment and reduce maintenance costs.

2、 How to choose better CAN Bus electrostatic protection devices

Firstly, a thorough understanding of the electrical characteristics of CAN Bus operation is required. CAN Bus typically operates within a specific voltage range, such as the commonly used 24V, so the selected electrostatic protection device must be able to operate normally within this voltage range. This requires us to have a clear understanding of the operating voltage, signal amplitude, transmission rate, and other parameters of the CAN Bus standard.

Secondly, the level of electrostatic protection is a key indicator for selecting electrostatic protection devices. Ensure that the selected devices provide sufficient electrostatic discharge (ESD) protection to cope with potential electrostatic shocks. Common protection level standards such as IEC 61000-4-2. Generally speaking, the higher the protection level, the stronger the device's ability to resist static electricity.

Thirdly, capacitance value is also an important factor that cannot be ignored. Due to the high signal integrity requirements of CAN Bus, if the capacitance value of electrostatic protection devices is too large, it may cause signal distortion, increased delay, and other problems, thereby affecting communication quality. Therefore, priority should be given to selecting protective devices with lower capacitance values to minimize the impact on CAN Bus signal transmission.

Fourthly, working voltage and clamp voltage are also important parameters to consider. The working voltage of the electrostatic protection device should be greater than or equal to 24V when the CAN Bus is working normally, to ensure that the device will not trigger incorrectly under normal working conditions. At the same time, the clamping voltage should be low enough to quickly limit excessive voltage within a safe range in the event of electrostatic discharge, thereby protecting the circuit components at the back end.

After understanding the above key points, we will make the correct choice when choosing CAN BUS anti-static ESD diodes.

1、 Comparison of Common Parameters of CAN BUS Electrostatic Diodes

The following is a list of parameters for several models of CAN BUS bus ESD protection circuits and common well-known brand CAN BUS electrostatic diodes

 CAN BUS electrostatic protection circuit

We conducted a detailed observation of this table and found several differences: IEC 61000-4-2 anti-static ability, power, VB, VC IPP, Cj.

Here, we specifically compare the three low clamp voltage (VC) CAN BUS static diodes from Shanghai Leimao in the table: SMC24XQ, SMC24LVQ，SMC24HQ。

Based on the previous analysis, we know that it is better to choose the one with a high to low static electricity ratio. The three SMC24 series from Shanghai Leimao are all 30KV, achieving the highest level of static electricity protection.

Anti static ability: The key to Shanghai Leimao's SMC24XQ, SMC24LVQ, and SMC24HQ is low VC, with all three VCs ranging from 32V to 34V, which is the lowest VC value on these lists. This is the most important parameter for selecting ESD diodes.

Clamping voltage VC: Shanghai Leimao SMC24 low VC series with three currents of 5A, 10A, and 13A can be selected according to the actual circuit situation, of course, the larger the current, the better. In addition, low clamping voltage and VC products are also available.

The junction capacitance Cj is also the lowest in the table, with 5PF and 15PF, which does not affect signal transmission and can fully ensure signal integrity.

Below is a presentation of the test chart for one of the SMC24LVQ models

If you are currently selecting CAN BUS static diodes or encounter issues with backend chips being damaged by static electricity, you can contact Shanghai Leimao EMC for selection guidance and further discussion.