Selection Guidelines for CAN TVS Solutions in Different Automotive Power Systems

In modern automobiles and various transportation vehicles, the application of electrical systems is becoming increasingly common. This phenomenon is becoming more apparent with the rapid development of technology. To enhance the safety and reliability of automotive systems, power management and subsystem protection design must be evaluated during system design to prevent damage to the system caused by high-energy transient events encountered at the signal end of the subsystem. This article mainly introduces how to select suitable electrostatic protection components according to the characteristics of different automotive power systems based on the ISO16750 automotive standard to ensure the stability and reliability of the subsystem. Subsequently, the electrostatic protection requirements of 12V and 24V voltage systems in the subsystem will be discussed, and corresponding component selection suggestions will be proposed. 

Potential Hazards of Electrostatic Discharge

Electrostatic discharge (ESD) refers to the electrical energy released by static electricity after it accumulates to a certain extent through a conductor or medium. This phenomenon is actually quite common in our daily lives, especially in dry environments; the generation and release of static electricity are more frequent. For automobiles, electrostatic discharge may cause irreversible damage to the internal electronic components of the vehicle, which may lead to system failure and even cause serious safety hazards. For example, for the electronic control unit (ECU) of a car, electrostatic discharge may cause data loss, system restart or failure to operate normally. These problems will directly affect the safety and performance of the vehicle. 

Electrostatic Protection Requirements for Different 12V & 24V Automotive Power Systems

12V & 24V voltage systems are the standard voltage systems used in most current cars and trucks. Different from consumer electronics, since automotive systems need to consider the characteristics of the battery and the requirements of automotive regulations, for 12V automotive systems, ESD protection components of 27V should be selected, and for 24V automotive systems, ESD protection components of 36V should be selected. The main reasons include the following: 

1. Working Voltage (VRWM)

It is necessary to pay attention to whether the VRWM of the selected protection component can be above the test voltage range of ISO16750 (for example, for a 12V system, select a protection component VRWM ≥ 27V, and for a 24V system, select a protection component VRWM ≥ 36V). 

2. Polarity (Uni/Bi-directional) 

Bi-directional TVS is suitable for use on bi-directional signals, and can avoid the component from being reversed, causing abnormal signal conditions. 

Uni-directional TVS is suitable for unidirectional signal sources, and can dissipate the energy of negative pressure more quickly. 

In automotive products, in addition to the difference in system voltage, it is still necessary to pay attention to the test specifications of automotive regulations. Since the CAN signal is a 5V signal level, if consumer electronic products are used to select protection components, 5V protection components are often selected on the CAN signal. However, in fact, it is necessary to pay attention to the test specifications of the automotive regulation ISO16750. In the ISO16750 Reversed voltage, the power supply may be accidentally touched on the CAN signal line during the jump start process. Therefore, bi-directional TVS must be selected on the CAN signal. The recommended part numbers are AZ9427-02S & AZ9436-02S.