汽车以太网的演进与保护：满足现代车辆数据需求

The automobile industry, a hotbed of innovation since the first motor vehicles hit the roads, has significantly evolved in recent years. This evolution, particularly in automotive Ethernet, is crucial for the industry's progress. Today's cars boast a plethora of features, including autonomous and semi-autonomous driving capabilities, automatic emergency braking, lane departure warning, Omni-View systems (surround-view system, Bird's eye system, etc.)  that eliminate blind spots, and a highly interactive and intuitive infotainment system. These innovations rely on a network of advanced cameras and sensors like radar, lidar, or image sensors to collect comprehensive information about the vehicle's physical environment. This data is then seamlessly conveyed to the driver through the dashboard display, alleviating their workload across various driving scenarios. 

Contemporary automotive systems demand fast and reliable communication networks to facilitate efficient data exchange. Traditional protocols like CAN (Controller Area Network) and LIN (Local Interconnect Network) have limited bandwidth, which has become inadequate for handling the growing data flow in modern vehicles. Automotive Ethernet solves this challenge and offers significantly higher bandwidth capabilities, enabling rapid transmission of large data volumes. Furthermore, it integrates essential functionalities required for automotive applications by combining time-sensitive networking with standard networking specifications.  

Ensuring reliable high-speed Ethernet communication in the demanding automotive environment is crucial. Enhancing these communications' reliability requires robust protection against electrical overstress (EOS) events. Electrostatic discharge (ESD) ranks at the top of conditions that cause EOS damage. Protecting electronic components from ESD threats while adhering to stringent automotive safety and reliability standards is essential. This blog post will explore how to fortify automotive Ethernet systems against ESD using protection devices that comply with OPEN Alliance specifications, a leading industry group focused on promoting Ethernet technology in automotive applications. First, let us investigate the automotive 2-wire twisted pair ethernet standards. 

2-Wire Twisted Pair Automotive Ethernet Standards 

Over a decade ago, a study by Broadcom showed that all inter-vehicle communications can be effectively done via an Ethernet interface that employs a single twisted pair of ethernet wires connected to a central switch. They pioneered a novel communication protocol called BroadR-ReachTM. This outperformed existing in-vehicle network protocols and seamlessly supported high-bandwidth applications in the challenging, noise-prone automotive environment. The BroadR-ReachTM has since been revised and adopted as an IEEE 802.3bw standard called 100BASE-T1.  

Figure 1. Full Duplex 2-wire twisted pair automotive ethernet operation

100BASE-T1 

100BASE-T1 employs a single unshielded twisted-pair cable to transmit and receive (Full Duplex) data over communication distances of at least 15 meters. This simplifies the interface to a single, twisted pair with universal applicability, significantly reducing cable numbers and cabling weight. The Full Duplex 2-wire twisted pair operation is shown in Figure 1. The OPEN (One Pair Ethernet) Alliance Special Interest Group (SIG) has established BroadR-Reach as the industry-standard physical layer, enabling its widespread adoption for automotive ethernet connectivity. BroadR-Reach, which later transitioned into the IEEE 100BASE-T1 standard under the guidance of OPEN Alliance SIG, marked the protocol's entry into automotive applications with a rate of 100Mbits/second. This data speed significantly boosted in-vehicle network efficiency, facilitating rapid data communication crucial for contemporary vehicle systems that demand high-bandwidth capabilities. 100BASE-T1 is generally used to connect ECUs, sensors, and cameras in modern vehicle support systems, such as infotainment and advanced driver-assistance systems (ADAS).  

1000BASE-T1 

The bandwidth potential of the automotive ethernet protocol received a significant boost with the advent of 1000BASE-T1, which delivered a remarkable tenfold increase in data rate to 1000Mbps or 1Gigabit per second. The standard of 1000BASE-T1 is based on IEEE 802.3bp specification. For automotive applications, 1000BASE-T1 leverages a cost-effective unshielded twisted-pair cable for data transmission and reception, reaching distances of up to 15 meters. This technology has the potential for extended reach in other applications. This substantial enhancement not only paved the way for the seamless integration of highly data-intensive automotive applications with cutting-edge features such as high-resolution cameras, LIDAR systems, and data-intensive ECUs but also hints at the exciting future potential of automotive Ethernet, fostering a sense of excitement and optimism about the industry's future.  

MGBASE-T1 

The automotive industry is experiencing an increasing need for high-speed data transmission, particularly in autonomous driving and safety systems. Modern vehicles rely on a centralized computer architecture that collects data from various sensors and components, necessitating higher bandwidth connections. To address potential data transfer bottlenecks, the industry has developed MGBASE-T1, an addition to the IEEE 802.3ch standard. This technology enables multi-gigabit speeds (2.5, 5, and 10 Gbps) over a single twisted-pair cable, effectively meeting the demand for faster in-vehicle networks. MGBASE-T1 is designed for short-range applications, with a maximum reach of 15 meters and up to four connection points, prioritizing electromagnetic compatibility and energy efficiency. 

10BASE-T1S  

The automotive ethernet protocol also includes 10BASE-T1S, designed for lower bandwidth needs, and runs at 10 Megabits per second. This particular Automotive Ethernet standard presents a practical solution for systems that require faster communication than existing protocols such as CAN-FD but don't require rapid data transfer rates such as 100BASE-T1S for cost and power reasons. In particular, IEEE 802.3cg defines the 10BASE-T1S, where "S" stands for a short length of 15-25m distance. Another standard, 10BASE-T1L, exists for a longer distance of 1km, but this standard is not used for automotive applications. 10BASE-T1S is on a single twisted pair, and it supports three different operating modes: 

• Point-to-point 15m with optional full duplex 

• Point-to-point 15m with mandatory half duplex 

• Multidrop 25m with optional half duplex 

This progression demonstrates how automotive Ethernet has adapted to meet the increasing data demands of modern vehicles, from basic connectivity to supporting advanced autonomous and safety features. Table 1 provides a comprehensive comparison of automotive ethernet standards from 10Mbps to 10Gbps, aiding in understanding the evolution of these standards. 

Table 1. Comparison of automotive ethernet standards

Safeguarding Automotive Ethernet with TVS Diodes from Semtech  

Despite the advancements in automotive Ethernet to handle the growing data demands of modern vehicles, these systems remain susceptible to voltage transients caused by load switching, inductive load kickback, and electrostatic discharge (ESD), potentially damaging sensitive components. To ensure the reliability and robustness of these systems, ethernet transceivers and related circuitry are commonly protected by Transient Voltage Suppression (TVS) diodes. These diodes are crucial in preventing potential damage from voltage spikes, acting as voltage clamps that divert excessive energy and safeguard sensitive components. Their presence is a testament to the industry's commitment to ensuring the safety and reliability of automotive Ethernet systems, providing a sense of security and confidence in the system's reliability. 

ESD protection as per OPEN Alliance 

TVS diodes are essential in automotive Ethernet to protect transceivers from damaging voltage transients. These TVS diodes also play a crucial role in meeting industry standards for electromagnetic compatibility (EMC). The OPEN Alliance sets guidelines for automotive Ethernet and recommends specific characteristics for ESD protection diodes to ensure reliable operation in harsh automotive environments. These guidelines include bi-directional operation of the TVS diode, an operating voltage above 24V, and an ESD trigger voltage of at least 100V. Furthermore, the guidelines specify that ethernet interfaces should be protected against ESD events up to ±15kV (contact) for unpowered devices according to ISO 10605 (discharge storage capacitor C=150pF and discharge resistor R=330Ω), and the TVS device should be able to withstand 1000 such discharges without damage. Refer to this blog to know more about the difference between IEC 61000-4-2 and ISO 10605 specifications. 

The OPEN Alliance also provides guidelines for the optimal placement of TVS diodes in automotive Ethernet systems. They recommend placing the TVS diode between the MDI (Medium Dependent Interface) connector and the common mode termination network, as illustrated in Figure 1. This method is referred to as "line-side" protection. In contrast, earlier automotive Ethernet designs typically placed the TVS diode between the CMC and the PHY, as shown in Figure 3, known as "PHY-side" protection. The advantage of line-side protection is that the TVS diode is positioned directly at the connector, providing protection not only for the PHY but also for the common-mode choke (CMC) and other passive components. The ESD surge would pass through the CM termination, DC block, and CMC in PHY-side protection before reaching the TVS diode. Due to this placement in different positions, the selection of TVS diode will also be varied. 

RClamp10022PWQ for line-side protection per OPEN Alliance specifications 

Semtech's RClamp10022PWQ (Figure 2) is a 2-line TVS diode designed for ESD protection of 100BASE-T1, 1000BASE-T1, and 10BASE-T1S automotive ethernet interfaces per OPEN Appliance specifications. RClamp10022PWQ is a bi-directional TVS diode with a trigger voltage greater than 100V. This part provides an operating voltage of 30V and a maximum clamping voltage of 38V at 6A peak pulse current.  

Figure 2. Line-side ESD protection per OPEN Alliance using RClamp10022PWQ 

RClamp10022PWQ features a maximum ESD withstand voltage of ±15kV (Contact), ±25kV (Air) as per the IEC 61000-4-2 standard, and ±15kV (air) and ±15kV (contact) as per the ISO 10605 standard (Test conditions: 150pF/330pF, 330Ω). RClamp10022PWQ is qualified for AEC-Q100, Grade 1, and AEC-Q101.  

This part is available in a 5-pin DFN package (2.0 x 1.0 x 0.55 mm) with side wettable flanks. Side-wettable flank technology ensures proper soldering by allowing automated visual inspection (AVI) systems to verify that ICs are reliably bonded to PCBs, enabling defect detection in automotive production lines. The device's flow-through package design simplifies the PCB layout and helps maintain signal integrity. RClamp10022PWQ can withstand at least 1000 contact discharges at ±15kV without damage. 

RClamp10022PWQ has a maximum junction capacitance of 0.6pF between I/O pins and GND. The junction capacitance vs. temperature curve is shown in Figure 3 (left). Low capacitance TVS diodes are critical for protecting automotive Ethernet and other high-speed signal lines from transient voltage spikes without degrading signal integrity. TVS diodes with low capacitance ensure minimal insertion loss and distortion, allowing high-frequency signals to pass through without interference. This is particularly important in automotive networks, where any increase in capacitance can slow signal transitions, cause reflections, and degrade overall system performance.  

RClamp10022PWQ utilizes a deep snapback or crow-bar technology shown in Figure 3 (right) to minimize device clamping voltage and features a high surge current capability of 6A (tp=1.2/50µs). Snapback or crow-bar technology in TVS diodes refers to a protection mechanism where the diode transitions to a low-impedance state when a specific threshold voltage is exceeded, allowing it to divert excessive current and protect sensitive electronic components from damage due to voltage spikes. By clamping the overvoltage and handling high surge currents, TVS diodes with snapback characteristics ensure long-term reliability and protection of circuits in harsh automotive environments. 

                             Figure 3. Junction capacitance vs. temperature (Left) and Deep Snapback characteristics (Right) of RClamp10022PWQ 

The OPEN Alliance standards require automotive ethernet components to pass rigorous EMC tests to ensure reliable operation in harsh automotive environments. These tests ensure compliance with industry standards for minimal interference, data integrity, and safe operation in real-world automotive environments. The RClamp10022PWQ passed all key standards tests and validation suites of key industry players and verification labs. 

RClamp0592PWQ for PHY-side protection 

Semtech's RClamp0592PWQ (Figure 4) is a 2-line TVS diode for PHY-side ESD protection of 100BASE-T1 and 1000BASE-T1 automotive Ethernet interfaces。 RClamp0592PWQ protects a two-line system with an operating voltage of 5V and a maximum clamping voltage of 6V at a 10A peak pulse current. This part features a maximum ESD withstand voltage of ±30kV (contact), ±30kV (air) as per the IEC 61000-4-2 standard, and ±25kV (air) and ±30kV (contact) as per the ISO 10605 standard (Test conditions: 150pF/330pF, 330Ω, 2kΩ). RClamp0592PWQ is qualified for AEC-Q100, Grade 1, and AEC-Q101. This part is designed in a 3-pin DFN package (1.0 x 0.6 x 0.55 mm) with side wettable flanks. RClamp0592PWQ utilizes snapback or crow-bar technology to minimize device clamping voltage and features a high surge current capability of 10A (tp=8/20µs).  

Figure 4. PHY-side ESD protection using RClamp0592PWQ

RClamp01892PWQ for PHY-side protection 

The RClamp01892PWQ (Figure 5) is a specialized ESD protection device engineered for high-speed automotive Ethernet interfaces specifically designed to protect the PHY-side of MultiGBASE-T1 connections. This compact device, housed in a 3-pin DFN package (1.0 x 0.6 x 0.55 mm) with side wettable flanks, safeguards two 1.8V data lines by implementing snapback technology to achieve a maximum clamping voltage of 5V at 2.5A peak pulse current. It offers robust protection against ±8kV contact ESD (per IEC 61000-4-2 standard) while maintaining exceptional signal integrity through its low 0.3pF typical capacitance. The device meets automotive reliability standards AEC-Q100 Grade 1 and AEC-Q101, making it a reliable choice for demanding automotive applications. 

Figure 5. PHY-side ESD protection using RClamp01892PWQ 

结论 

The evolution of automotive Ethernet reflects the dramatic transformation in vehicle technology, from basic networking to today's sophisticated requirements for autonomous driving and advanced safety systems. As vehicles incorporate increasingly complex features and generate larger data volumes, automotive Ethernet standards have evolved from 10Mbps (10BASE-T1S) to 10Gbps (MultiGBASE-T1) to meet diverse needs. However, these high-speed networks require robust protection mechanisms, particularly TVS diodes in line-side and PHY-side configurations, to safeguard sensitive systems against ESD events and other transient threats to ensure reliable operation. Solutions provided by Semtech, like the RClamp10022PWQ, demonstrate how modern protection devices can meet stringent OPEN Alliance specifications and deliver the highest levels of robustness while maintaining signal integrity. As automotive technology advances with the need for ever-increasing data rates for high-speed data transmission, implementing rugged protection mechanisms remains crucial for ensuring the safety and reliability of next-generation vehicles. This requires manufacturers and designers to prioritize performance and protection in their automotive applications. 

To learn more about Semtech's product offerings for the automotive industry, please visit https://www.semtech.com/products/circuit-protection/automotive. 

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