Getting Started With the Ethernet Switch

This project implements a multi‑port Ethernet switch with a 2.5 Gbps SFP uplink and a separate gigabit uplink. The base switch IC is the VSC7426 from Microchip, which provides 12 fast‑Ethernet PHYs and integrates an MIPS processor for management functions. An additional VSC8574 expansion PHY extends the number of ports, and a serial port allows console access.

Functional Overview

The points below describe the main building blocks of the switch. Understanding how the switch IC, PHYs, memory and power supplies interact will help you design your own custom switch.

• Port configuration – There are twelve 10/100 Mbps ports, one 1 Gbps uplink and a 2.5 Gpbs SFP cage for optical or copper modules. The VSC7426 switch interfaces to the SFP via a high‑speed SerDes, while the VSC8574 provides additional copper PHYs.
• Management and memory – The integrated MIPS CPU in the VSC7426 runs the switch firmware. External DDR2 memory and SPI flash store configuration and boot code.
• Power delivery – Multiple regulators generate 1.0 V, 1.8 V, 2.5 V and 3.3 V rails for the switch core, PHYs and I/O. Decoupling capacitors and ferrite beads are placed near each power pin to suppress noise and maintain power integrity.

How To Use This Ethernet Switch

The instructions in this section explain how to power and configure the switch. They cover connecting the Ethernet ports, using the SFP uplink and accessing the console.

• Power the board – Apply the specified DC input voltage (typically 5 V or 12 V depending on the design). Onboard regulators will generate the required voltages. Ensure adequate cooling for the VSC7426 and expansion PHY.
• Connect Ethernet ports – Plug RJ45 cables into the 12 fast‑Ethernet ports. Use the SFP cage for fiber or high‑speed copper modules to connect to a backbone network. The gigabit uplink can be used for direct connection to a router or server.
• Console and configuration – Use the serial port to access the management interface. Configure VLANs, QoS and other switch settings through the command‑line interface or via firmware API.

Design Considerations

High‑speed switching requires careful attention to routing, signal integrity and power distribution. The recommendations here address these challenges.

• BGA fan‑out and routing – The VSC7426 and VSC8574 are large BGA packages with many differential pairs. Use microvias and escape fan‑out to route signals from the inner rows. Maintain controlled impedance on all SerDes and RGMII pairs and place AC‑coupling capacitors near the switch pins.
• SFP interface and termination – The SFP receiver and transmitter lines are AC‑coupled. Place the coupling capacitors at the switch side, and use 50 Ω traces with the correct length matching. No Bob Smith termination is needed because the SFP module manages its own common‑mode termination.
• PDN and decoupling – Provide a solid ground plane and separate power planes for each voltage. Use arrays of decoupling capacitors and ferrite beads near the power pins to reduce noise. Ensure the DDR2 and flash have their own decoupling networks to maintain signal integrity.
• Power sequencing – Follow the recommended power‑up sequence for the VSC7426 and expansion PHY. Use reset and power‑good supervisors to guarantee that rails ramp in the correct order.

By following high‑speed PCB design practices, including controlled‑impedance routing, tight length matching and robust power delivery, this project can be adapted to create custom Ethernet switches for industrial control, telecom or data‑center applications.

In addition to the high‑speed routing, thermal management is an important consideration. The VSC7426 and expansion PHYs dissipate significant heat during operation; use copper pours and thermal vias under the packages to conduct heat to the opposite side of the board or to a heatsink. Select SFP modules rated for 2.5 Gbps operation and ensure that the supply rails meet their power requirements. Implement VLANs and port isolation through firmware to tailor the switch for specific network configurations, and use the serial console for debugging and firmware updates.

Additional Resources

Read the full guide article on Altium Resources for a deep dive on this project. The video below shows the design approach and bringup of the Rev A release of this project. Additional videos show important work on AC coupling capacitor placement on high-speed differential lines and the grounding strategy typically used in Ethernet-enabled devices with magjack RJ-45 connectors.