"Radar sensors are always damaged by static electricity" "The battery management system fails the load rejection test" "Signal attenuation occurs after high-speed bus protection" ... These problems may seem scattered, but they all point to the core threats of on-board electronics - electrostatic discharge (ESD) and transient power rail impacts. 

Based on 15 years of experience in protection and in-depth research on the vehicle's electrical environment, Shanghai Lebao has specifically developed a "power-supply - signal - layout" three-in-one protection system. This system has now covered core modules such as BMS, domain controllers, and intelligent cabins. Today, starting from actual working conditions, the EMC expert from Lebao will disassemble and explain how to build an "all-round protection net" for the vehicle's ECU. 

1. First, understand the threats to vehicle electrical systems: The two most lethal types of shocks 

In the vehicle-mounted environment, the electrical shocks faced by electronic modules have specific scenarios. Through thousands of tests, we have concluded that the following two types are the top priorities for protection: 

Data cable: "Instant Assault" of 25kV static electricity

The vehicle-mounted data cables (CAN/LIN bus, radar/camera signal lines) are most prone to ESD impacts - when passengers touch the vehicle doors or maintenance personnel plug or unplug connectors, ±25kV air discharge (equivalent to breaking a 3mm air gap) and ±8kV contact discharge may occur, with the voltage rising time ≤ 1ns. These "short, fast, and intense" pulses will directly break through the input pins of the vehicle's MCU, causing communication interruption. 

For such risks, Le Maou has set the following protection standards: The ESD protection level must reach ISO10605 Category 3 level 4, with an air discharge requirement of ±25kV, and the clamping voltage (Vc) must be lower than the maximum tolerance voltage of the vehicle-mounted module (usually 45V), while not affecting the signal transmission. 

2. Power rail: 87V transient "continuous bombardment" 

What is even more challenging than ESD is the transient condition of the power supply rails, especially in two typical scenarios:

Inductor load power-off (pulse 2a): When the relay is disconnected, the inductor of the wiring harness will generate a 37-50V sharp voltage peak that lasts for 50 microseconds, which is equivalent to giving the 12V power supply system a "high-voltage slap", and is likely to burn out the ECU power chip.

Load sudden drop (pulse 5a): When the battery suddenly disconnects while the generator is still generating electricity, a high voltage of 65 to 87V will be generated, lasting for up to 400ms. This shock is particularly fatal to the battery management system (BMS) and has caused cases where the BMS's data collection accuracy deviated by more than 10%. 

The protective targets stipulated by the standard are very clear: In the ISO 7637-2 test, the transient voltage must be stabilized within the safe range, while ensuring that the device does not overheat or its parameters do not drift under continuous impact. 

II. Lei Ma's Three Core Solutions: Targeted Solutions to Address the Pain Points of Vehicle Protection 

Based on a thorough analysis of vehicle-mounted threats, we have developed three core protection solutions, corresponding to the three major aspects of power input, signal link, and PCB layout. Each solution has undergone rigorous testing and verification: 

Power Input: SM8S series TVS diodes, used as "voltage safety valves"; 

Regarding the transient conditions of the power supply rails, the SM8S series TVS diodes of Lai Mou are the core protective components. Their key parameters perfectly match the requirements of the vehicle.

Voltage Adaptation: For the 12V vehicle power supply system, Lebao uses SM8S24CA. The reverse working voltage is 24V. When charging the battery, the peak output voltage of the generator can reach 15V. A safety margin is reserved to prevent the device from malfunctioning. For the 24V vehicle system, Lebao uses SM8S33CA. It meets the ISO7637-2 5A/5B test for pre-installed vehicles and the ISO10605-2 standard, level 4, with contact discharge of 15KV and air discharge of 25KV. 

High transient tolerance: For example, in the 87V load sudden drop test of the 12V system, SM8S24CA can clamp the voltage to 38.9V (≤ the maximum tolerance voltage of the ECU), with a peak power of 6600W;

· Vehicle-grade reliability: Certified by AEC-Q101, capable of operating in a wide temperature range of -55℃ to 175℃. 

When combined with the Lei Ma PPTC self-recovery fuse, it can also provide "clamping + overcurrent" dual protection, effectively dealing with the combined impact on the power supply rail. 

2. Signal Link: Low Junction Capacitance Series ESD Diodes, when "Signal Guardian" 

The key challenge in data cable protection lies in "preventing ESD while not affecting the signal". Lei Ba has perfectly resolved this contradiction by selecting the appropriate low-lead-capacitance ESD diodes that match the different signal rates:

Low capacitance and low clamp voltage: less than 5pF, lower than the requirements for high-speed signal transmission (≤10pF). Suitable for 100Mbps vehicle Ethernet, CAN FD and other buses. The measured signal attenuation is ≤0.5%, without affecting the data transmission rate.

High ESD protection: Contact discharge ±30kV, Air discharge ±30kV. This exceeds the basic protection requirements for vehicles. Even in rainy weather, it can ensure the purity of signals for precision sensors such as radars and cameras. 

Small package advantages: Using SOT-23 packaging, the board area occupied is only 2.9mm × 1.6mm, suitable for high-density layout of vehicle ECU. 

3. PCB Layout: Li Baou's "3mm + Symmetry" principle, eliminating parasitic issues. 

Often, the failure of protection measures is not due to the device itself, but rather a hidden danger caused by the PCB layout - every 35μm copper track per centimeter will generate 5nH of parasitic inductance, and under a 12.5A current impact, the additional voltage drop can reach 62.5V, directly nullifying the protective effect. Lei Ma summarized this as the "3mm + Symmetry" layout rule: 

3mm distance principle: The distance between the protective device and the connector should be ≤ 3mm. This minimizes the surge path and reduces the measured parasitic inductance from 5nH to 1.5nH, with an additional voltage drop reduction of 70%. 

Symmetrical wiring design: The wiring length from protective devices to data lines and to ground should be within ±0.5mm. The additional voltage caused by Ldi/dt should be offset. The surge response time should be controlled within 1ns to ensure that transient shocks are quickly clamped.

III. From Testing to Mass Production: Practical Validation of the Lebao Solution 

Le Ma has a laboratory in Shanghai. All the plans have undergone dual checks of "scenario testing + mass production verification": 

Scenario-based testing: Simulate full vehicle operating conditions for shock, such as applying ±25kV ESD discharge to the ECU equipped with the Leibo solution. After the test, the ECU's communication was normal and there were no functional abnormalities; an 87V load suddenly dropped for 100ms, and the device parameters did not drift. 

Production stability: Capable of providing large-scale supplies to automakers at a rate of 100,000 units per year. The delivery cycle is only 2 weeks (compared to an industry average of 6-8 weeks), significantly reducing the inventory pressure on customers. 

Customer Case: After adopting the Lebao TVS solution for the BMS module of a leading new energy vehicle manufacturer, the ESD test pass rate increased from 70% to 100%. After the load sudden drop test, the communication interruption time was controlled within 5ms (much lower than the 50ms functional safety requirement). 

Conclusion: Lei Ma, the "safety partner" in automotive electronics 

Vehicle-mounted protection is not simply a collection of components; it is a system solution based on scenarios. Lei Mou has always started from the actual needs of the automakers, using 15 years of protection experience to refine the products and optimize the solutions, all in an effort to ensure that the electronic systems of every new energy vehicle can be protected from electrostatic surge threats. 

Leiditech Electronics is committed to becoming a leading brand in electromagnetic compatibility solutions and component supply, offering products such as ESD, TVS, TSS, GDT, MOV, MOSFET, Zener, inductors, etc. Leiditech has its own free laboratory and has an experienced R&D team, which can provide personalized customization services according to customer needs and offer the best solutions for customers.