Robust ESD protection for automotive Ethernet: addressing the needs of 10BASE-T1S and beyond

10BASE-T1S, in particular, is gaining momentum for its ability to connect multiple nodes over a single unshielded twisted pair (UTP) cable. This offers a cost-efficient and space-saving alternative to traditional point-to-point architectures, making it ideal for body domain controllers and sensor networks. However, the rise of these systems introduces new demands, particularly for effective and application-appropriate electrostatic discharge (ESD) protection.

Table 1. Overview of automotive Ethernet standards

Balancing high voltage tolerance and signal integrity

Designing ESD protection for Ethernet-based automotive networks presents a set of interrelated challenges. One primary concern is that components must support high trigger voltages. The OPEN Alliance mandates that ESD protection devices for UTP-based Ethernet interfaces maintain a trigger voltage above 100V. This high threshold prevents devices from activating unintentionally during electromagnetic compatibility events, which are frequent in environments where Ethernet wires share space with power lines and other signal carriers.

Another challenge involves minimising parasitic capacitance. In 10BASE-T1S networks, where up to 50 nodes may share a single cable, excessive capacitance can compromise signal integrity. Therefore, ESD devices must be designed to keep capacitance well below one picofarad.

Clamping voltage behaviour is equally critical. During an ESD event, the protection device must effectively limit the voltage reaching the system without allowing harmful electrical energy to damage sensitive transceivers. Devices that clamp too high may fail to protect the system adequately.

Durability is also essential. Automotive systems must function reliably over long service lifetimes in harsh operating conditions. An ESD protection component that deteriorates after repeated discharges threatens consistent performance and long-term reliability.

Lastly, compatibility with Power over Data Line (PoDL) systems is required. Ethernet implementations that combine data and power over the same twisted pair need protection components that can tolerate continuous exposure to up to 48V or more without leaking or breaking down.

Defining a new class of ESD protection for automotive Ethernet

Modern ESD protection for Ethernet interfaces must address all these requirements while maintaining signal integrity and ensuring long-term reliability. Among the technologies available today, silicon-based snap-back diodes have proven particularly effective. These devices compare favourably with traditional varistor-based alternatives.

While Ethernet variants such as 10BASE-T1S, 100BASE-T1, and 1000BASE-T1 differ in speed and physical configuration (see Figure 1), they share a common set of protection requirements. Devices are expected to meet several critical specifications: trigger voltage should exceed 100V, while standoff and holding voltages (VRWM and VH) must remain above 24V. ESD robustness is defined by the ability to withstand contact discharges of 15kV across at least 1,000 strikes. In addition, devices should exhibit controlled clamping behaviour and minimal residual current. For 10BASE-T1S in particular, parasitic capacitance should not exceed two picofarads (2 pF), and the optimal threshold is considerably lower.

Higher trigger voltages are essential in applications using UTP cabling, which lacks the shielding of shielded twisted pair (STP). In contrast, STP cables used in some 1000BASE-T1 implementations provide shielding effectiveness that may exceed 40dB. This additional protection reduces susceptibility to electromagnetic interference, allowing for a broader range of ESD device specifications, including lower trigger voltages.

Figure 1. Unified schematic for 10BASE-T1S, 100BASE-T1, and 1000BASE-T1 interfaces

While the overall topology remains consistent, with UTP cables, standard connectors, and similar layout, key variations exist in transceiver characteristics, common-mode choke (CMC) specifications, and termination resistor values.

Technology comparison: varistor vs. silicon

Varistors, such as metal-oxide varistors (MOVs), have long been used as basic ESD suppressors. Their straightforward design and inherently low capacitance make them an easy choice for many circuits. However, their high and often inconsistent clamping voltages and a tendency to degrade under repeated ESD strikes limit their effectiveness in modern automotive systems. These characteristics make them unsuitable for protecting sensitive Ethernet transceivers in high-reliability applications.

Silicon-based snap-back devices, by contrast, offer a more robust solution. They provide high trigger voltages, often around 140V, and lower clamping voltages near 40V. This performance minimises the risk of downstream damage. Their capacitance can be engineered to remain below 0.4pF, making them particularly well-suited for 10BASE-T1S networks. Most importantly, these devices maintain their protective properties across repeated ESD events, preserving signal integrity over time.

Real-world application: Nexperia’s PESD1ETH10L-Q series

As an example of this class of ESD protection, these devices are designed to meet the requirements outlined by the OPEN Alliance. They feature a standoff voltage VRWM of 75V and a typical device capacitance of 0.35pF. Their trigger voltage of approximately 140V and clamping voltage near 40V place them well within the target range for high-speed, low-noise automotive applications.

These devices are available in compact DFN1006 package formats. The PESD1ETH10LS-Q variant includes side-wettable flanks, making it compatible with automated optical inspection processes. Additional package variants are being developed to support a range of design configurations.

Table 2. Nexperia’s PESD1ETH10L-Q series

Testing conducted at an independent laboratory confirms the performance of the PESD1ETH10LS-Q across key criteria. Due to the device's low capacitance, mixed-mode S-parameter tests show strong results for return loss, insertion loss, and mode conversion. Further testing demonstrated that the device withstood 8kV contact discharges without performance degradation. Residual current evaluations based on IEC 61000-4-2 15kV pulses confirmed that the silicon-based design meets Class III standards. Comparable tests with varistors frequently show violations of these limits (see Figure 2).

Figure 2. Residual current from varistors clearly exceeds the ESD device limits defined by the OPEN Alliance

Support for PoDL architectures

The IEEE 802.3bu standard outlines PoDL capabilities with voltages up to 48V delivered over a single Ethernet pair. In practice, this means that ESD protection devices must handle continuous exposure to elevated voltages without leakage or premature clamping.

Devices with a standoff rating VRWM of 75V, like those in Nexperia’s portfolio, can protect PoDL circuits in current-generation vehicles and systems that anticipate future voltage increases. This voltage tolerance simplifies circuit design in zonal architectures where one cable may carry both power and communication signals. As shown in Figure 3, which represents a typical industry-benchmark PoDL topology for automotive Ethernet, the ESD protection device is directly exposed to the full voltage delivered from the Power Sourcing Equipment (PSE) to the Powered Device (PD). Thanks to their 75V VRWM rating, devices like the PESD2ETH10LS-Q and PESD2ETH10L-Q offer robust and future-proof protection in such configurations.

Figure 3. PoDL topology for automotive Ethernet

Conclusion: moving toward a unified protection strategy

The adoption of Ethernet in vehicles brings new requirements for electromagnetic resilience. Effective ESD protection is essential not just for compliance but for maintaining the long-term performance and safety of automotive electronics.

Silicon-based protection solutions offer a compelling balance of low capacitance, high trigger voltage, consistent clamping behavior, and robustness under stress. By selecting components that meet these criteria, engineers can future-proof their Ethernet architectures.

Nexperia’s PESD1ETH10L-Q series is a strong example of how such devices can support 10BASE-T1S, 100BASE-T1, and 1000BASE-T1 applications while meeting stringent automotive standards, including those for PoDL operation. These solutions are part of a broader trend toward unified, reliable, and scalable in-vehicle networking.