Construction-wise, an industrial PC is not much different from a typical desktop PC and both of them are running on X86-based CPUs (from Intel and AMD), except that the industrial PC is all about stability, compatibility and expandability. For this, an industrial PC does not require transmission at I/O port as fast as in a consumer PC. On the other hand, an industrial PC requires reliability, longevity and robustness to external interference, as it is usually used in an environment mush harsher than that of a consumer PC, such as factory, railway application and on board a ship. Therefore, a lot of attention is placed on the ESD/surge protection at I/O port to keep ESD/surge from causing I/O port malfunction.
The Ethernet port transmission has been upgraded from 1Gbps to Ethernet 2.5Gbps in mainstream IPC chip designs and 2.5Gbps has been adopted as standard design as major industrial PC manufacturers are working on their new projects. However, it often occurs to them that the designed 2.5Gbps chips fail the ESD/surge test due to the chips’ susceptibility to ESD/surge. This article is written to present a complete ESD/surge protection solution for Ethernet 2.5Gbps.
Ethernet 2.5Gbps consists of primarily 4 differential pairs of signals; the transmission is as fast as 625Mbps for each differential pair, which means that the capacitance cannot be too high for ESD/surge protection device, as it may lead to signal anomaly. An Ethernet surge test is performed in common mode (line to ground) and differential mode (line to line). For ESD/surge test in common mode, the four-channel TVS array protection device is recommended. The recommended solution is AZ1213-04F in DFN2510P10E package. Thanks to the unique packaging, the PCB layout is designed using Feed through, which makes the design much easier. AZ1213-04F has a signal-to-ground parasitic capacitance of 2.1pF (Typ.) and is capable of resisting the 20A energy of an IEC61000-4-5 surge (8/20μs). With a surge (8/20μs) at 20A, the surge clamping voltage is approximately 7.5V, whereas the ESD clamping voltage is around 6.5V at 16A (ESD=8kV). Figure 1 presents the surge clamping voltage and TLP I-V curves of AZ1213-04F.
Figure 1. Surge clamping voltage and TLP I-V curves of AZ1213-04F
For the surge protection for differential mode (line-to-line), the AZ5B0S-01F in DFN0603P2Y (0201) package is recommended, as it features a parasitic capacitance of 0.18pF (Typ.) and robustness to IEC61000-4-5 Surge (8/20μs) 7A energy. With surge (8/20μs) at 7A, the surge clamping voltage is approximately 4V. Figure 2 provides the surge clamping voltage I-V curve of AZ5B0S-01F.
Figure 2. Surge clamping voltage I-V curve of AZ5B0S-01F
Apart from the AZ5B0S-01F mentioned above for surge protection in the differential mode, there is the AZ522S-01F in DFN1006P2E(0402) package. It has a parasitic capacitance of 0.2pF (Typ.) and robustness to IEC61000-4-5 Surge (8/20μs) 6.5A energy. With the surge (8/20μs) at 6.5A, the surge clamping voltage is roughly 5V. Figure 3 shows the surge clamping voltage I-V curve of AZ522S-01F.
Figure 3. Surge clamping voltage I-V curve of AZ522S-01F
In addition to the protection devices for common mode (line to ground) and differential mode (line to line), it is commonly seen that energy is coupled to LED control signal and causes LAN PHY damage as the system is subject to ESD and surge tests. It is rather important to have protection for LAN LED control signal wire. It is recommended to have a protection device along the LED control signal wire as a precaution. Figure 4 provides the complete protection circuitry for 2.5Gbps Ethernet protection.
Figure 4. 2.5Gbps Ethernet ESD/EOS protection circuitry
It is recommended to take ESD/surge protection into consideration in the initial design stage of system circuitry, since it is mentioned above that an industrial PC is likely to expose to harsh environment. This makes 2.5Gbps Ethernet port more robust against functional failure due to ESD/surge at the network port as the system is used in the end market.