The transmission requirements and data payload on automotive networks has and continues to increase significantly. To take the next step we need high-speed, high-bandwidth Automotive Ethernet, and that means getting the right ESD protection in place to ensure it is both safe and secure while we are driving. With System-Efficient ESD Design (SEED), new system-level approaches to ESD simulation have helped develop new protection components that meet industry requirements.
As mentioned in a previous blog, ‘OPEN Alliance: Get the right ESD protection placement’, to support the rising demands of high data-rates, data security, and flexibility we need to move away from heterogeneous in-vehicle networks (LIN, CAN-FD and FlexRay) to a homogeneous Ethernet architecture.
One key goal of the OPEN Alliance (One-Pair Ether-Net) Special Interest Group (SIG) is to enable the deployment of the existing IEEE 100BASE-T1 and 1000BASE-T1 physical layer specifications with complementing specifications for conformance and interoperability. To achieve that while addressing the unique operating conditions in cars led to placing the ESD protection device immediately next to the connector – rather than between the common-mode choke (CMC) and the PHY – protecting not only the PHY but also the CMC and passives.
In its document ‘IEEE 1000BASE-T1 EMC Test Specification for ESD Suppression Devices’, the OPEN Alliance proposes a measurement called ‘ESD Discharge Current Measurement’. This gives an estimation of the overall system-level ESD robustness. This test determines the residual current into the PHY, identifying the ESD robustness class according to human body model requirements.
SEED provides system-level approach to ESD
A fundamental ESD design challenge is the prediction of system level robustness. A general misconception is that system level robustness depends on the robustness of individual components. Instead, it depends on several factors:
- the robustness of the weakest device in the system (usually the SoC that is to be protected)
- the properties of the protection device
- properties of other elements in the signal path
- parasitic effects arising from the board and mounting wires
The concept of SEED (as outlined in Chapter 5 of the ESD Application Handbook – Protection concepts, testing and simulation for modern interfaces) is to consider all these parameters as an equivalent circuit or circuit-like simulation to predict system level robustness. An equivalent circuit representation of the system, including the SoC, is connected with a model of the protection device to evaluate protection performance. As well as SPICE-based simulations, other simulation tools such as Verilog-A and customized models based on network parameter blocks can be combined realize the system simulation.
OPEN Alliance Ethernet ESD protection
When developing the industry’s first silicon-based, OPEN Alliance-compliant ESD protection for 100/1000BAASE-T1 automotive Ethernet systems, Nexperia used System-Efficient ESD Design (SEED) methodology to replicate the ESD Discharge Current Measurement test.
By using the SEED methodology, Nexperia was able to investigate how different parameters, including the parasitic inductance of the external ESD protection device, its trigger and snap-back behavior, influence the system level ESD robustness. It also enables developers to predict the levels of electromagnetic stress that other passive devices are exposed to during an ESD event. A full description and explanation of how the methodology was applied can be found in our whitepaper: Efficient prediction of ESD discharge current according to OPEN Alliance 100BASE-T1 specification using SEED.
The result is the first true OPEN Alliance-compliant ESD protection for 100/1000BASE-T1 Ethernet. Silicon devices offer a significantly higher level of protection - up to 30kV system level robustness – than older technologies such as varistors, which are also subject to degradation over time. Available in low-cost, small, SOT23 surface-mounted plastic packages, the PESD2ETH100-T and PESD2ETH1G-T are the first choice for modern automotive Ethernet interfaces.