ESD protection design in automotive electronic circuits

Automotive electronics is currently a hot development area, and the booming development of the Chinese automotive market has brought new opportunities to the local automotive electronics industry. More and more companies have increased their investment in automotive electronics, and localized design and manufacturing companies of a large number of automotive electronics, including ECU, ABS, DVD, GPS, HVAC, and CANBUS, have mushroomed. This also opens up a new world for electronic component manufacturers engaged in circuit protection design.

Safety and reliability are essential

A fuse is a type of passive passive device that resembles a switch. In the event of a product failure or an accident, the fuse is required to be safely disconnected in the power supply section without generating smoke/open flames, and not to endanger the life of the operator. Therefore, no matter what kind of electronic products, fuses are usually configured without exception, and it is also a guarantee for the safety of electronic products.

For fuses, the most important reference is safety and reliability, that is, it can never be disconnected during normal operation, and must be disconnected immediately when the fault occurs in the latter stage. The fuse has only two operating states: on or off. To ensure the safety and reliability of the entire system, the fuse itself must first meet these two points. Good fuse design is essential and an ingenious science.

When designing a fuse, circuit designers should consider two main aspects: static and dynamic. Static refers to voltage, current, ambient temperature, size, failure current, etc.; dynamic refers to the melting time, melting heat value, etc. These are the key points in the design of fuse products. Secondly, after the theoretical calculation of the fuse, it is necessary to combine the on-site test and verification, and finally achieve the ideal design by means of reliability analysis.

Innovative automotive circuit protection design

The circuit protection inside the car is everywhere, especially now that the car body uses more and more intelligent electronic devices, turning the former pure car machinery into a "running robot" with a soul. For electronic products, safety is paramount, and fuses in automotive circuits are thus integrated and miniaturized.

In the development of automotive electronics, almost every electrical device requires a fuse, commonly referred to as cable protection. The main function of the fuse is to limit the increase of current. When an accident occurs (such as a short circuit fault caused by a car accident), the large current generated at this time requires the fuse to cut off the main power immediately to avoid further danger. The traditional car cable fuse has a multi-pole and layered protection structure, but when the next-level electronic device fails, only the faulty unit fuse is broken without affecting the upper-level circuit. . However, in the process of car modification, for example, when a high-powered sound is added externally, the power is taken from the body battery. If the fuse is not used properly, it will not be disconnected when it needs to be disconnected, and it will be affected by these small faults. The reliability of the vehicle system causes the fuse to malfunction, so good fuse design and selection is especially important.

Littelfuse's latest circuit protection product for automotive controller area network (CAN) applications.

To this end, the innovative integrated fuse (Masterfuse) is integrated into the design of automotive electronics, which combines the overall over-current protection of the body to achieve a higher level of protection. The integrated fuse product is a configurable fuse solution with a variety of different fuse types (ie MEGA and MIDI) and ratings in a compact package. This packaged fuse allows the user to replace multiple discrete fuses in the distribution box with one component, eliminating the bolts, busbars and cables currently required. By reducing the number of connectors required, the overall system increases reliability while reducing costs, and each integrated fuse can be customized to the user's application for an optimized circuit protection package.

Integrated fuse

On the other hand, there is also a class of synchronous overvoltage protection devices TVS that are equally worthy of attention. Because in automotive electronics, all electronic devices are exposed to electrostatic (ESD) and LOADDUMP threats. These overvoltage problems can cause permanent damage to the chip circuit, so overvoltage protection is essential and at the same time, These requirements are also part of the ISO7637 standard. In this respect, Littelfuse automotive grade TVS tubes meet the above requirements to ensure the safety and reliability of automotive electronics. In fact, the application of TVS has become more common, and the long-life, high-reliability operating state is a must-have performance of automotive-grade TVS, such as AEC-Q101 certification, to meet the requirements of vehicle operation.

Taking the automotive electronic ESD protection scheme as an example, due to the large number of applications of the buttons and the USB interface, the test specifications are continuously upgraded, and the electrical protection requirements of the ISO10605 standard are even up to 25KV. Without a reliable circuit protection device, this requirement cannot be met. Littelfuse's semiconductor protection arrays can meet the ESD test requirements of the entire circuit. For example, the SP1003 can achieve 30KV test specifications, and each circuit is connected in parallel with a protective device to protect the car electronics. In addition, in terms of data line protection, the wide application of CAN bus in the car connects all the electronic components together for data exchange. For the protection of CAN chip, Littelfuse's special protection device provides an ideal protection form, which can not only meet ESD protection. At the same time, it can meet some surge protection requirements. For example, the typical application circuit of the SM24CANA series provides dual protection of common mode and differential mode.