Learn how TVS diodes protect industrial RJ45, PoE, and CAN interfaces from surge and ESD strikes, improving communication system stability and EMC immunity.
Application Background
As industrial automation systems increasingly rely on high-speed communication, Ethernet protocols such as EtherCAT, PROFINET, and Modbus TCP have become standard in PLCs, servo drives, industrial gateways, and remote I/O units. These interfaces are often deployed in electrically noisy environments, where lightning surges, inductive switching transients, and ESD from cable handling pose serious threats to reliability. TVS (Transient Voltage Suppression) diodes are widely adopted to protect Ethernet interfaces due to their ultra-fast response and robust energy absorption capabilities.
Working Principle & Benefits
A TVS diode is typically connected between signal lines and ground. When a transient spike occurs, the diode switches into low-impedance mode in nanoseconds, clamping the voltage and redirecting excess energy away from sensitive downstream components like Ethernet PHYs or SoCs.
Key benefits include:
Sub-nanosecond reaction time
Compact packages suitable for integration inside RJ45 or magnetics
Low-capacitance models maintain signal integrity on differential pairs
Compliance with IEC61000-4-2 and IEC61000-4-5 standards
Design Guidelines
Design notes:
Use ultra-low capacitance TVS arrays (<1pF) on differential pairs to avoid signal distortion
Select high-energy TVS for power pins (PoE, 48V), with surge ratings >30A
Place TVS devices close to RJ45 to minimize parasitic inductance
Use Case
An industrial gateway supporting EtherCAT and Modbus TCP integrated TVS protection for each RJ45 port. Two differential lines were protected with low-capacitance TVS arrays, and PoE power pins had high-energy TVS devices. The unit passed ±15kV ESD and ±2kV EFT testing and was successfully deployed in smart factories.
Conclusion
TVS diodes are indispensable for protecting industrial Ethernet interfaces against surges and ESD. They enable compliance with EMC standards and enhance the durability of mission-critical communication equipment. As networks grow faster and more compact, TVS protection will remain a core design consideration.
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