USB 3.1 to Gigabit Ethernet Adapter Hardware Design - Phil's Lab #174

Why It Matters

This design shows engineers how to add gigabit Ethernet to USB‑3.1 devices cheaply and quickly, accelerating product development for high‑speed networking in compact hardware.

Key Takeaways

• USB‑3.1 to Gigabit Ethernet board uses Microchip LAN780 transceiver.
• Simple bus‑powered design needs only 3.3 V regulator and minimal components.
• Integrated magnetics in RJ45 jack eliminates external transformers, saving space.
• Six‑layer PCB from JLCPCB costs $2 for 5 pcs, fast turnaround.
• Driver support spans macOS, Windows, Linux; OTP memory programmable via MPAB.

Summary

The video walks through design of a USB‑3.1 to Gigabit Ethernet adapter PCB built around Microchip’s LAN780 transceiver, showing how a simple, bus‑powered board can deliver 1 Gbps Ethernet over a USB‑C/Type‑B connection.

The schematic is minimal – a 5 V USB input, a buck regulator to 3.3 V, the LAN780 QFN48, and an integrated RJ45 mag‑jack with LEDs. The designer highlights power budgeting (≈256 mA at 3.3 V for full‑speed operation), decoupling (1 µF per pin, bulk caps), and the use of low‑capacitance ESD protection on USB‑3.0 lines. The board also includes a programmable OTP via MPAB configurator.

Notable details include the choice of a six‑layer PCB from JLCPCB at $2 for five 50 × 50 mm boards, the integrated magnetics that remove external transformers, and cross‑platform driver availability (macOS, Windows, Linux). The presenter notes that the USB‑3.1 spec permits swapping differential pair polarity, simplifying routing, and that the design follows Microchip’s hardware checklist.

For hardware developers, the example demonstrates that high‑speed USB‑3.1 to Ethernet conversion can be achieved with low component count, inexpensive prototyping, and rapid time‑to‑market. The design principles—proper power filtering, careful impedance‑controlled routing, and leveraging integrated magnetics—are directly applicable to IoT gateways, edge devices, and custom compute modules.

Original Description

Schematic, PCB design, and testing of a custom USB 3.1 SuperSpeed to Gigabit Ethernet adapter based on the Microchip LAN7800. Covers high-speed differential routing, controlled impedance, and more Altium.

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[LINKS]

LAN7800 Datasheet: https://ww1.microchip.com/downloads/en/DeviceDoc/LAN7800-Data-Sheet-DS00001992G.pdf

LAN7800 HW Design Checklist: https://ww1.microchip.com/downloads/aemDocuments/documents/UNG/ProductDocuments/DesignChecklist/LAN7800-HW-Design-Checklist-00003446.pdf

[TIMESTAMPS]

00:00 Intro

02:15 JLCPCB (Ad)

03:50 Altium Develop (Ad)

05:13 Schematic

18:41 PCB Overview, Stack-up, and Controlled Impedance

22:46 PCB Layout and Routing

33:14 Configuring OTP/EEPROM

38:18 Speed Test

39:59 Outro