一、Profinet Introduction

1. Origin and position

PROFINET is an industrial Ethernet standard led by Siemens and promoted by the PROFIBUS Users' Organization (PI). IT was officially released in 2001, aiming to address the limitations of traditional PROFIBUS buses in high-speed real-time communication, cross-vendor compatibility, and IT/OT integration. PROFINET couplers, as the "bridge devices" of PROFINET networks, are core components for the integration of traditional fieldbuses (such as PROFIBUS) and PROFINET Ethernet, supporting the implementation of "distributed control" and "intelligent interconnection" in Industry 4.0. At present, the protection requirements of mainstream coupler models (such as Siemens IM 154-8 and Phoenix FLM PN) can all be met with compliance adaptation through the ESD/TVS devices of Leiditech Electronics.

2. Classification and Application

PROFINET couplers can be classified by function into protocol conversion type (such as Siemens IM 154-8, which realizes the mutual conversion between PROFIBUS and PROFINET), integrated IO type (such as Phoenix FLM PN, with built-in IO terminals for direct connection to sensors), and redundant enhancement type (such as Hersman SPIDER) Supports dual network port redundant switching, compact types (such as Weidmuller UR20, suitable for narrow Spaces), etc.

The core functions include protocol conversion and real-time data transparent transmission (ensuring the control instruction cycle is ≤1ms), network expansion (cascading support for 126 slave stations), diagnostic monitoring (locating faults through indicator lights or software), and distributing 24V DC power to downstream low-power devices. It is widely applied in scenarios such as automotive manufacturing (welding and assembly line robot communication), food and beverage (filling equipment networking), logistics and warehousing (AGV interaction), energy and chemical (pump and valve control), etc., and is compatible with the hybrid network architecture of traditional equipment upgrades and intelligent factories. Shanghai Leiditech has developed a mature selection library of protection devices based on the electromagnetic interference characteristics of different scenarios, which can quickly match the interface protection requirements of couplers.

二、Protective background and core standards

1. Risk of electromagnetic interference in industrial environments

PROFINET couplers installed in industrial sites (such as workshops, control cabinets, and outdoor cabinets) are exposed to multiple interferences:

• Electrostatic Discharge (ESD) : Static electricity from the human body when the operator comes into contact with the interface or the equipment casing, or induced static electricity in a dusty/dry environment, may cause damage to the interface chip (such as Ethernet PHY, PROFIBUS transceiver).
• Surge: Lightning electromagnetic induction (transmitted through power lines/communication lines) and switching surges (transient voltages can reach several kV) generated by the start and stop of motors/frequency converters, which may cause communication interruption or hardware burnout.
• The EMC guy from Shanghai Leiditech emphasized that the interference in industrial sites is often a superposition of "ESD + surge", and a two-level protection architecture of "discharge + clamping" should be adopted to avoid protection failure caused by the failure of a single component.

2. Core standards

• Electrostatic protection: IEC 61000-4-2 (Contact Discharge/Air Discharge), industrial equipment must meet Grade 3 (contact ±6kV/air ±12kV) or Grade 4 (contact ±8kV/air ±15kV, high-risk scenarios).
• Surge protection: IEC 61000-4-5 (1.2/50μs voltage wave, 8/20μs current wave), power interface must meet grade 3 (wire-ground ±4kV), communication interface must meet grade 3 (wire-line ±2kV).
• Industry-specific additional requirements: The automotive industry (such as the VDA standard) demands higher redundancy and must pass the level 4 surge test; Due to the cleaning requirements (water rinsing) in the food industry, it is necessary to enhance the static electricity protection of the outer shell.

三、Shanghai Leiditech's protection solutions for each interface

（一）Signal port protection: Precisely match the signal characteristics of PROFINET

1. Ethernet interface RJ45 (10/100Mbps)

PROFINET relies on TX+/TX- and RX+/RX - differential lines, which require separate protection and control of parasitic capacitance. The Leiditech solution complies with IEC61000-4-2, grade 4, with contact discharge ±30kV and air discharge ±30kV. IEC61000-4-5 10/700μs, 40Ω, ±6kV, ±5 times. This solution ensures no packet loss during high-temperature transmission.

• First-level discharge: The interface side is connected in series with the Thunderbolt 3R900-5S gas discharge tube (GDT), with a breakdown voltage of 90V±20% and a current capacity of 10kA (8/20μs), which can discharge 90% of the surge energy and prevent large currents from affecting the subsequent chips.
• Two-stage clamping: Each pair of differential lines is connected in parallel with Leiditech GBLC03C ESD diode (SOD-323 package), with a clamping voltage of ≤20V (compatible with the withstand voltage of PHY chips such as TI DP83848 and Weixin LAN8742), and the single-channel capacitance is only 0.6pF, with no signal distortion.

Leiditech EMC guy added: Differential line protection requires strict control of the total sum of "parasitic capacitance of devices + PCB trace capacitance". The low capacitance characteristic of GBLC03C is the key to ensuring the integrity of 100Mbps signals.

2. The RS485 auxiliary interface (equipment configuration/diagnosis) of Leiditech Electronics uses P0080SC TSS in parallel with the A/B signal lines and between the signal lines and ground. The TSS response time is at the nanosecond level, which can not only prevent surges and static electricity, but also ensure signal integrity. Complies with IEC61000-4-2, static electricity class 4, contact discharge ±8kV, air discharge ±15kV; IEC61000-4-5 Surge 10/700μs, ±6KV;

Leiditech EMC guy reminds: RS485 cables in industrial workshops are often laid parallel to power lines. It is recommended to series a current-limiting resistor at the front end of P0080SC to further reduce the impact of surge current on TSS protection devices.

3. USB auxiliary interface

The Leiditech adopts a single SR05W device to protect the USB2.0 interface, saving space and ensuring signal integrity. It meets IEC61000-4-2, grade 4, with a contact discharge of ±8kV and an air discharge of ±15kV, guaranteeing various electrical interferences for industrial customers. If there is an overcurrent requirement for the Vbus, a PTC should be used in combination to achieve dual protection of "overvoltage + overcurrent".

（二）Power port protection: Blocking surge intrusion into the core circuit

For 24V industrial power supplies (the main intrusion path of surges), Shanghai Leiditech has designed a triple protection of "overvoltage + overcurrent + backflow prevention" :

• Overvoltage protection: The positive and negative terminals of the power input are connected in parallel with Leiditech SMBJ26CA TVS diodes. The clamping voltage is ≤42V (24V power supply safety threshold), with a current-carrying capacity of 14.3A (10/1000μs), enabling rapid discharge of transient overvoltage.
• Overcurrent protection: Series Leiditech self-resetting fuse (PPTC) automatically disconnects in case of overcurrent (such as short circuit), and resumes after the fault is eliminated to prevent the power module from burning out.
• Anti-reverse connection: Polarity reverse connection protection is achieved by using PMOS (suitable for high-power scenarios above 20A, recommended is the LM5D28P10 type PMOS from Leiditech Electronics) or low-dropout Schottky diodes (suitable for low-power scenarios, such as Leiditech Electronics SK56C, 60V/5A).

（三）PCB design optimization: Ensuring protection effect and signal integrity

1. Layering and impedance design

An 8-layer symmetrical stack (signal layer → ground plane → signal layer → ground plane → power layer → ground plane → signal layer → signal layer) is adopted to ensure that all signal layers are adjacent to the complete ground plane, reducing the electromagnetic coupling path through the continuity of the ground plane.

·         The impedance control of high-speed differential lines (such as Ethernet and RS485) is 100Ω±5% (verified through simulation based on the characteristics of FR-4 plates), and the line length matching error is ≤25mil, reducing signal reflection and coupling with external interference.

2. Layout of protection and filter devices

·         The protective devices (GDT, TVS) should be adjacent to the interface pins (with a distance of no more than 3mm), and the grounding path should adopt a 0.5mm via array (≥4) directly connected to the ground plane to shorten the interference discharge path and reduce the impact of parasitic inductance on surge suppression. Shanghai Leiditech EMC guy suggests: The via array should be evenly distributed around the protective device to avoid forming a "single-point grounding bottleneck".

3. Grounding and shielding design

·         The interface ground (RJ45/RS485 housing) is safely connected to the ground directly through metal screws and sawtooth washers (impedance < 1Ω). The system signal ground and safety are connected at a single point using 2mm wide copper foil to avoid interference introduced by ground loops.

·         The metal casing and the PCB ground plane are electromagnetically sealed at 360° through conductive pads and metallized vias. The shielding efficiency in the 100 MHZ to 1GHz frequency band is ≥60dB, reducing the penetration of external electromagnetic interference.

Shanghai Leiditech Electronics is committed to becoming a leading brand in electromagnetic compatibility solutions and component supply, offering products such as ESD, TVS, TSS, GDT, MOV, MOSFET, Zener, inductors, etc. Leiditech has an experienced R&D team that can provide personalized customization services based on customer needs and offer the most superior solutions to customers.