Modern motor vehicles have been aptly described as computers on wheels. Manufacturers worldwide are adapting Ethernet-based networks as the standard for vehicular intra-communications. But the automotive environment is a harsh one, with extremes in temperature, humidity, and most of all, electrical noise.
The PESD2ETH100-T and PESD2ETH1G-T. Image (modified) used courtesy of Nexperia
Nexperia’s new electrostatic discharge (ESD) protection devices are targeted at providing vital ESD protection in this challenging environment.
Basics of the ESD Protection Devices
The PESD2ETH100-T and the PESD2ETH1G-T are targeted at 100BASE-T1 Ethernet and 100/1000BASE-T1 Ethernet, respectively. They both provide ESD protection of up to 30 kV as per IEC 61000-4-2 for contact discharges. The devices will provide protection for up to 1000 contact discharges at that 30 kV level.
Automotive communications cable may come in contact with the car battery’s voltage, and in any case, they are likely to be subject to high-power, common-mode noise. For these reasons, the devices are designed with ESD trigger voltages of greater than 100 V.
Graphic symbol for Nexperia’s ESD protection devices. Image used courtesy of Nexperia
Because the device must provide ESD protection without degrading high-speed signal integrity, they must offer low parasitic capacitance. The maximum values for the PESD2ETH100-T and the PESD2ETH1G-T are 3 pF and 2 pF, respectively.
Both devices are available in 2.9 mm by 1.3 mm by 1 mm SOT23 packages and are AEC-Q101 qualified.
According to Dr. Jan Preibisch, Netscape application marketing manager, “By design of the norm, the Nexperia ESD protection solutions PESD2ETH100-T and PESD2ETH1G-T work with any PHY. Our devices provide outstanding robustness at high data rates without showing degradation like other technologies.”
Electrical and Physical Characteristics
The PESD2ETH100-T and the PESD2ETH1G-T feature several electrical and physical characteristics that make it stand out from other ESD protection devices like them.
- Reverse stand-off voltage at 25℃ is 24 V
- Rated peak pulse current is 2.3 amperes
- Reverse leakage current is 100 nA
- The device operates over a temperature range of -55℃ to +150℃
What is the OPEN Alliance?
Nexperia is a technical member of the OPEN Alliance.
The OPEN Alliance is a non-profit special interest group (SIG) composed of automotive industry and technology providers. Its purpose is to advocate for the wide-scale adoption of Ethernet-based networks in automotive networking applications and to establish Ethernet as an industry-wide standard.
Members are also involved in the complete ecosystem for automotive networking, including the cable harnesses, switches, and electronic control units.
Reconsidering ESD Protection Device Placement
PHY vendors have previously recommended that the protective device be placed between the PHY and the common mode choke (CMC). With that methodology, an ESD strike would pass through the CM termination, DC blocking capacitors, and common mode choke (CMC), likely damaging them.
According to Lukas Droemer, product manager for Nexperia’s automotive ESD protection & filtering portfolio, the change advocated by the OPEN Alliance involves placing the ESD protection right at the connector, as illustrated below.
New proposed ESD protection methodology. Image used courtesy of Nexperia
With this new proposed methodology, the ESD protection device is placed right at the connector. It now not only protects the PHY but also the passives and the CMC.
What design methods have you used with ESD protection devices? Share your thoughts in the comments below.