Gigabit Ethernet Low Residual Voltage, High Current Solution Reference
This solution is a Gigabit Ethernet standard solution from VOOHU Electronics Technology. The company has focused on the field of communication electronic components for over 8 years, adhering to the business strategy and service philosophy of "Choose VOOHU, truly reliable," and providing complete technical solution support.

More product information on this website:
 Standard Circuit Design Reference for 10 Gigabit Ethernet Lightning Protection & Static Electricity Protection Solutions

100Mbps Ethernet surge protection and anti-static standard circuit

I. Technical Background and Core Concepts

1.1 Low Residual Voltage, High Current
- Low Residual Voltage: Refers to the low residual voltage (typically <20V) remaining across the protective device after conduction, ensuring the protected chip is not damaged by high voltage.
- High Current: Refers to the protective device's ability to instantaneously handle high surge currents (typically >50A, 8/20μs waveform), rapidly dissipating energy.
- Core Contradiction: Traditional TVS diodes have low residual voltage but low current capacity, while high current results in high residual voltage; special design is needed to balance these two factors.

1.2 Why Ethernet Needs This Technology
Ethernet interfaces are exposed to the external environment and are susceptible to:
- Lightning-induced surges (outdoor equipment)
- Power supply crosstalk (industrial environment)
- Electrostatic discharge (ESD) (human contact)
- Power Line Connection (Construction Fault)

II. Detailed Technical Solution

(Current-Type) Solution Advantages:
Electrostatic Discharge Protection Features: Gigabit Ethernet port electrostatic discharge protection, using multi-channel integrated devices, high ESD protection, small size, low capacitance, ensuring signal integrity, meeting the following standards: IEC61000-4-2 (ESD) ±30KV (air), ±30KV (contact), IEC61000-4-4 (EFT) 40A (5/50ns); IEC61000-4-5 (Lightning) 32A (8/20μs).
Lan Transformer Features: Small size, low height. Turns ratio 1:1; Open circuit inductance: 350 uH; Insertion loss: -1.1 dB Max, DC resistance 1.3Ω.

1. Primary Side Wiring:
• Differential Pair Connection: Connect the differential pairs TD0/TD1 and RD0/RD1 to the primary side of the lan transformer. The pin order of the four differential pairs can be interchanged during PCB routing.
• Decoupling Capacitor: The primary side should be connected to GND through a 100nF capacitor to ensure signal stability and integrity.
• VCC Power Supply: For current-mode PHYs, the primary coil needs to be connected to the PHY's VCC to filter high-frequency noise and ensure signal stability. It is recommended to connect two 49.9Ω resistors in parallel between each differential pair and connect them to GND.

2. Secondary Side Wiring:
• RJ45 Connection: The two sets of transmit and receive differential signals on the secondary side should be connected to pins 1, 2, 3, 6 and 4, 5, 7, 8 of the RJ45 interface, respectively.
• BOB Smith Circuit: Connect a 75Ω resistor to the secondary side, and then connect it to the chassis ground through a 1nF capacitor with a withstand voltage of 2KV or higher. 1206 packaged surface-mount ceramic capacitors or high-voltage ceramic capacitors with a wide lead pitch are recommended.

3. Grounding Treatment:
• Floating Pins: The floating pins of the RJ45 interface should also be connected to the chassis ground via a similar design, ultimately flowing into the earth to ensure the integrity of the entire circuit's grounding system. Circuit Function Description
• BOB Smith Circuit: A circuit consisting of a 75Ω resistor and a 1nF capacitor provides a return path for common-mode signals, effectively filtering out common-mode signals, improving electromagnetic interference (EMI), and suppressing inrush current to some extent.
• Decoupling Capacitor: A 100nF capacitor is used to filter out high-frequency noise, ensuring signal stability and integrity.
• Voltage Rating Capacitor: The 1nF capacitor must have a voltage rating of 2KV or higher to ensure reliability under high-voltage environments.



Advantages of the solution:

Electrostatic Discharge Protection Features: Gigabit Ethernet port electrostatic discharge protection, employing multi-channel integrated devices, high ESD protection, small size, low capacitance, ensuring signal integrity, meeting the following standards: IEC61000-4-2 (ESD) ±30KV (air), ±30KV (contact), IEC61000-4-4 (EFT) 40A (5/50ns); IEC61000-4-5 (Lightning) 32A (8/20μs).
Lan Transformer Features: Small size, low height. Turns ratio 1:1; Open circuit inductance: 350 uH; Insertion loss: -1.1 dB Max, DC resistance 1.3Ω.

1. Primary Side Wiring:
• Differential Pair Connection: The primary side of the lan transformer is connected to differential pairs TD0/TD1 and RD0/RD1 respectively. The wiring sequence of the four differential pairs can be interchanged during PCB routing.
• Decoupling Capacitor: A 100nF capacitor should be connected to GND on the primary side to ensure signal stability and integrity.

2. Secondary Side Wiring:
• RJ45 Connection: The two sets of transmit and receive differential signals on the secondary side should be connected to pins 1, 2, 3, 6 and 4, 5, 7, 8 of the RJ45 interface, respectively.
• BOB Smith Circuit: A 75Ω resistor should be connected to the secondary side, followed by a 1nF capacitor with a withstand voltage of 2KV or higher, connected to the chassis ground. 1206-package surface-mount ceramic capacitors or high-voltage ceramic capacitors with wide lead pitch are recommended.

3. Grounding Treatment:
• Floating Pins: The floating pins of the RJ45 interface should also be connected to the chassis ground using a similar design, ultimately flowing into the earth to ensure the integrity of the entire circuit's grounding system. Circuit Function Description
• BOB Smith Circuit: A circuit consisting of a 75Ω resistor and a 1nF capacitor provides a return path for common-mode signals, effectively filtering them, improving electromagnetic interference (EMI), and suppressing inrush current to some extent.
• Decoupling Capacitor: A 100nF capacitor is used to filter high-frequency noise, ensuring signal stability and integrity.
• Voltage Rating Capacitor: The 1nF capacitor must have a voltage rating of 2KV or higher to ensure reliability under high-voltage conditions.



VOOHU Recommended complementary products for the solution:


III. Typical Application Scenarios
Intelligent Transportation Systems (ITS)
Scenarios: Intersection cameras, electronic police systems
Industrial Internet of Things (IIoT)
Scenarios: Factory automation, robotics
New Energy Power Generation
Scenarios: Photovoltaic inverters, wind power transformers
Data Centers and 5G Base Stations
Scenarios: Edge computing nodes, AAU/RRU


IV. Design Verification and Testing Standards
4.1 Key Test Parameters


4.2 Residual Voltage Measurement Techniques
Use a differential probe with a bandwidth > 500MHz to avoid ground loops.
The measurement point must be at the PHY chip pin, not at the TVS terminals.
Use an 8/20μs current source to inject current and simulate a real surge waveform.
Note: The above solutions are standard designs for reference only. The final circuit design will be based on site requirements. Contact us for free in-depth support.   
             Tel: 400-1048-018; E-mail: wohu@wohu-tek.com;

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