With the rapid advancement of technology, automotive electronics—such as infotainment systems, Advanced Driver Assistance Systems (ADAS), and camera modules—are becoming increasingly sophisticated. These applications demand higher signal bandwidth, faster data transmission rates, and lower latency. Traditional in-vehicle networks such as CAN and CAN-FD can no longer meet the requirements for high-quality audio and video. In contrast, Automotive Ethernet, with transmission speeds of 10/100/1000 Mbps, perfectly addresses these needs.
This article will focus on ESD/EOS protection solutions for Automotive Ethernet 100BASE-T1 and 1000BASE-T1.
Requirements from Open Alliance
The Open Alliance provides specific design guidelines for Automotive Ethernet: ESD protection devices should be placed directly behind the connector, followed by other components such as termination resistors, common-mode chokes, and capacitors.
Since Automotive Ethernet cabling typically uses UTP (unshielded twisted pair), the transmission lines are more susceptible to external EMI interference, which can result in voltages up to around 100V appearing on the signal lines. For this reason, the Open Alliance specifies that the trigger voltage of ESD devices must be ≥ 100V.
Below are the ESD protection requirements defined in the Open Alliance 100/1000BASE-T1 specifications:
1. Operating voltage ≥ 24V
2. Device must be bi-directional
3. ESD trigger voltage ≥ 100V
4. ESD device must withstand >15kV (ISO 10605, C = 150 pF, R = 330 Ω)
5. ESD device must survive at least 1000 strikes at 15kV (ISO 10605, C = 150 pF, R = 330 Ω)
Beyond electrical requirements, the Open Alliance also emphasizes signal integrity and effective protection. Parameters such as Sdd11 (Return Loss), Sdd21 (Insertion Loss), and Ssd21 (Differential-to-Common-Mode Rejection) must remain within limits before and after ESD events. Likewise, current levels after ESD strikes must remain within defined protection thresholds. Clearly, the Open Alliance sets very strict requirements for ESD devices. (See Figure 1 for an example Automotive Ethernet ESD protection circuit.)
Figure 1. Automotive Ethernet ESD protection circuit example
ESD Solutions for Automotive Ethernet
Solution 1: Dual-Channel ESD Protection Device – AZ9400-02S
Packaged in a standard SOT23-3L, the AZ9400-02S features a low parasitic capacitance to ground of 0.9 pF (Typ.), ensuring signal integrity. It offers ESD trigger voltage ≥ 100V and withstands ±30 kV contact discharge per IEC 61000-4-2 (150 pF/330 Ω). It can handle surge energy of 2.4 A (8/20 μs) per IEC 61000-4-5. At 16 A (equivalent to IEC 61000-4-2 ESD 8 kV), the clamping voltage is approximately 50 V.
Solution 2: Single-Channel ESD Protection Device – AZ9400-01F
Packaged in an ultra-compact DFN1006P2E (1.0 mm × 0.6 mm, 0402), the AZ9400-01F also provides a low capacitance of 0.9 pF (Typ.). It has the same trigger voltage of ≥ 100V, withstands ±30 kV IEC 61000-4-2 contact discharge, and handles surge current of 2.4 A. At 16 A (IEC 61000-4-2, 8 kV), the clamping voltage is approximately 46 V.
| Part Number | AZ9400-01F | AZ9400-02S |
| Working Voltage | ±24 |
±24 |
| Directional | Bi-Directional |
Bi-Directional |
| ESD Trigger Voltage | ≥100V | ≥100V |
| ESD robustness against damage | >±30kV | >±30kV |
| Minimum number of dischargers (15kV) | >1000 | >1000 |
| Cap. (Typ.) | 0.9pF | 0.9pF |
| Package Type | DFN1006P2E | SOT23-3L |
Both solutions are AEC-Q101 qualified and certified to meet Open Alliance requirements for 100BASE-T1 and 1000BASE-T1. Designers can select based on PCB space and design preferences.
Conclusion
Automotive environments are harsh, and without robust ESD protection, electronic modules risk damage or malfunction, potentially leading to severe safety hazards and negatively impacting brand reputation. ESD protection has therefore become a critical focus in automotive electronics. As a trusted partner, Amazing Microelectronics continues to develop automotive-grade protection devices and functional IC solutions, while working closely with OEMs and Tier 1 suppliers to anticipate and meet the evolving needs of the automotive industry.