Advanced circuit protection for connecting autonomous vehicles

At the beginning of this century, automobiles were equipped with many basically independent electronic systems. Since then, the growth of connectivity and the rise of artificial intelligence and machine learning have dramatically changed automotive electronics. Various types of vehicles have become complex, interconnected communication centers, and the capabilities of autonomous vehicles will only increase this level of complexity.

V2V and V2I vehicle power and communication circuits require fuses, PPTC, TVS diodes and diode arrays, MLV and polymer ESD suppressors for overcurrent, ESD and surge protection. V2X modules may use AQ3045 back-to-back TVS diodes manufactured with proprietary silicon avalanche technology to provide ESD protection to protect electronic equipment that may be subject to destructive electrostatic discharge (ESD). These diodes can safely absorb repeated ESD shocks to the maximum level (± 30 kV contact discharge) specified by the IEC 61000-4-2 international standard without degrading performance. When AC signals are present, the back-to-back configuration provides symmetrical ESD protection for the data lines. (An example solution from Littelfuse.)

New protocols are being deployed to enhance connectivity while promoting broadband-like automotive communications. V2X technology is designed to help vehicles communicate with the road and each other to prevent collisions and optimize traffic flow. Automotive versions of Ethernet and HDBaseT are being implemented to increase the speed and efficiency of high-speed data transmission between key subsystems, including HD cameras, lidar and radar sensors, and wireless connectivity.

Better connectivity makes cars safer and more versatile, but it also poses many technical challenges for engineers designing cars. More advanced automotive chipsets must also become smaller and denser, so they are more susceptible to electrostatic discharge (ESD). Design engineers must understand how to protect these chipsets to ensure their reliability.

Highly sensitive chipsets and the need for faster data require excellent ESD protection for automotive modules using these new protocols. Low-capacitance, low-clamp ESD protection devices in compact packages can help make advanced automotive operations safe, reliable and efficient.

To provide the engineering community with a unified and repeatable ESD mitigation plan, an ISO 10605 document was created. The severity of the ISO 10605 ESD pulse is sufficient to ensure that the chipset is unsustainable when subjected to a direct shock. For a robust and reliable design, engineers should consider ESD protection solutions early in the design process. In addition, engineers should review and understand the system-level ESD testing required for these modules.

ISO 10605 simulates human discharge inside or outside a vehicle. It specifically includes ESD during assembly, ESD caused by service personnel, and ESD caused by passengers. ISO 10605 is based in part on IEC 61000-4-2, a standard for system-level ESD immunity. However, it has some key regulations for automotive use. On the one hand, ISO 10605 does not define a specific upper limit for the stress voltage. For direct contact discharge, the test voltage is usually in the range of 2 kV to 15 kV, and for test discharge through the air gap is usually in the range of 15 kV to 25 kV. In addition, some automakers have designed their own ESD stress levels-some parts can be specified up to 30 kV contact and 30 kV air gap discharge.

The ISO 10605 test uses two different resistances, 2kΩ and 330Ω, to simulate different types of ESD events. The 2kΩ resistor represents the human body discharging directly through the skin, while the 330Ω resistor simulates the human body discharging through a metal object. The test was also performed on two different capacitors: 150 pF and 330 pF. These values represent the human body inside and outside the vehicle, respectively. The 330 pF and 330 Ω tests are the highest energy / current of any ISO 10605 test parameter and are therefore the most widely used test standards.

Manufacturers of ESD protection solutions are specifically designed to handle components for special automotive modules. It may be useful to consider some examples

Connected vehicles will carry "vehicle-to-vehicle (V2V)" and "vehicle-to-infrastructure (V2I)" communication modules that enable vehicles to perform tasks such as dynamic calculations based on the speed and position of other vehicles. One of the goals of the technology is to prevent vehicles from hitting other vehicles or pedestrians, smooth the flow of traffic and speed up the search for parking spaces, and may promote location-based advertising and promotions. American DoT believes that V2V communication can prevent up to 79% of vehicle crashes.

Typical ESD protection equipment for V2X modules is designed to suppress fast-rising ESD transients of up to 30 kV, with almost no increase in circuit capacitance. This is important for maintaining signal integrity on high-speed communication lines that are increasingly characterizing the use of automotive connections. Important. These two-way surface-mount polymer devices, named under the trade names PulseGuard or Xtreme-Guard, are designed to turn on fast enough at a voltage low enough to prevent damage to the protected parts.TVS diodes are also designed for high-speed Ethernet networks and are now optimized for automotive environments. High-speed Ethernet will allow multiple in-vehicle systems (such as infotainment and automated driver assistance systems) to simultaneously access high-bandwidth data throughput over a single unshielded twisted-pair cable.

Automotive Ethernet can achieve 100 and 1,000 Mbps communication using only two communication lines. Similar to Ethernet, HDBaseT has access to ADAS, telematics, A / V and display applications. HDBaseT provides throughput speeds up to 2 Gbps and can also move data to 15 m (50 ft) without losing data integrity. The protocol can also transmit multiple data types, including audio / video, USB / PCIe, Ethernet, control signals, and even power on the same data pair.

The CAN bus with a baud rate of 40kb / sec to 1 Mb / sec does not have enough bandwidth to handle the most advanced autonomous vehicle systems. Nonetheless, CAN and LIN bus systems will continue to play an important role in automotive electronic systems. CAN and LIN data lines can be protected from ESD and other overvoltage transients through devices such as the SM24CANB TVS diode array. The SM24CANB series can absorb repetitive ESD shocks exceeding the maximum level specified in the IEC 61000-4-2 international standard without degrading performance, and can safely consume 10A of 8/20 µsec inrush current at a low clamping voltage (IEC 61000 -4-5 Second Edition).

Looking ahead, HDBaseT will provide higher throughput, making it also regarded as the data backbone. It is expected that it will eventually handle speeds of 4, 8, 12, and 16 Gbps. Highly sensitive chipsets and the need for faster data will require excellent ESD protection. Low-capacitance, low-clamp ESD protection devices in compact packages will help make advanced automotive operations safe, reliable and efficient.

Automotive HDBaseT data lines can use ESD protection in the form of AQ255NUTG, which is a low-capacitance TVS diode array. It can also prevent light-induced surges in CDE (cable discharge event), EFT (electrical fast transient), and high-speed differential data lines. It is packaged in a µDFN package (3.0x2.0 mm), and each component can protect up to four channels or two differential pairs with a maximum protection of 45 A (IEC 61000-4-5 second edition) and a maximum of 30KV ESD (IEC 61000-4-2). The "thru-through" design minimizes signal distortion, reduces voltage overshoot, and simplifies PCB design.