How to Connect USB 3.0 PHY to Gigabit Ethernet Controller

The ASIX AX88179 is a USB 3.0 to Gigabit Ethernet controller. It uses USB 3.0 bandwidth and can send up to 5 Gbps of data. It works with many devices for fast network connections. The chip has a USB 3.0 host controller and a Gigabit Ethernet MAC inside. It supports IPv4 and IPv6 and has hardware acceleration. It also has low-power modes, built-in security, and VLAN tagging. The chip has a built-in RJ-45 port with LED lights. It comes with a datasheet and an SDK. These help you write drivers and make sure it works on different operating systems.

Core Logic: USB 3.0 PHY and Gigabit Ethernet Controller (like MAC) use different protocols. You must use a bridge chip or a SoC with both USB and Ethernet to convert the protocols. You cannot connect them directly. Here are two working solutions:

Solution 1: Use a USB-to-Ethernet Bridge Chip

Recommended Chip

• Model: ASIX AX88179 (USB 3.0 to Gigabit Ethernet)
• Features:
  • Has built-in USB 3.0 controller + Gigabit Ethernet MAC/PHY.
  • Supports IEEE 802.3az Energy-Efficient Ethernet.
  • Needs no external PHY.

Connection Diagram

USB 3.0 Host (PC/SoC)  
   │  
   ├── USB 3.0 Type-A/C port  
   │  
AX88179 Bridge Chip  
   │  
   ├── RGMII/MII port (optional, usually has built-in PHY)  
   │  
RJ45 port → Ethernet network  

Key Steps

1. Circuit Connection:
   • USB pairs: D+/D- and SSRX/SSTX connect directly to the host.
   • Ethernet: Bridge chip drives RJ45 directly (with built-in transformer).
   • Reference design:
     https://www.asix.com.tw/images/product/AX88179/AX88179_Block_Diagram.png
2. PCB Rules:
   • USB 3.0 traces: Match 90Ω impedance, length difference <5mil.
   • Keep Ethernet traces away from high-frequency noise.
3. Software Driver:
   • Linux: Use built-in ax88179_178a driver.
   • Windows: Use ASIX official driver.

Documents

• AX88179 Datasheet
• Reference Schematic

Solution 2: Use a SoC with USB + Ethernet MAC

Recommended SoC

• Model: NXP i.MX8M (has built-in USB 3.0 controller + Gigabit Ethernet MAC)
• Connection Logic:

USB 3.0 PHY (external)  
    │  
    ├── ULPI/UTMI/PIPE port  
    │  
i.MX8M SoC  
    │  
    ├── RGMII port  
    │  
External Ethernet PHY (e.g., Realtek RTL8211F)  
    │  
    └── RJ45  

Key Ports

1. USB 3.0 PHY Connection:
   • Port Type: PIPE 3.0 (standard for USB 3.0 PHY).
   • Signals: TX/RX_DATA[7:0], TX/RX_CLK, RESET.
2. Ethernet MAC Connection:
   • Port Type: RGMII (best for Gigabit).
   • Signals: TXD[3:0], RXD[3:0], TX_CLK, RX_CLK, MDIO, MDC.

Steps

1. PHY Selection:
   • USB 3.0 PHY: e.g., TUSB1310A (TI).
   • Ethernet PHY: e.g., RTL8211F (Realtek).
2. Circuit Connection:
   • USB PHY ↔ SoC: Follow PIPE 3.0 rules.
   • SoC ↔ Ethernet PHY: RGMII trace length ≤50mm, length difference ±100mil.
3. Software Setup:
   • Start USB controller (set as Host/Device mode).
   • Enable Linux Ethernet driver (e.g., fec or dwc_eth).

Documents

• i.MX8M Manual (Chapter 12: USB, Chapter 13: Ethernet)
• TUSB1310A PHY Datasheet
• RTL8211F PHY Datasheet

Important Notes

1. Signal Quality:
   • USB 3.0 and RGMII are high-speed (≥1Gbps). Do impedance and length matching.
   • Use 4+ layer PCB with solid ground plane.
2. Power Design:
   • USB PHY needs separate 3.3V/1.8V power (use low-noise LDO).
   • Ethernet PHY needs 1.2V core power + 3.3V I/O power.
3. Clocks:
   • USB 3.0: Give 24MHz clock (±50ppm).
   • Ethernet: PHY needs 25MHz crystal.
4. ESD Protection:
   • USB port: Add ESD diode (e.g., IP4234CZ6).
   • RJ45 port: Use transformer with 2kV ESD rating.

Debug Tools

• USB Analyzer: TotalPhase Beagle USB 5000.
• Ethernet Tester: Wireshark + Tcpdump.
• Signal Tools: Keysight ADS (simulate high-speed signals).

For all solutions, follow the chip maker’s reference designs. Using a bridge chip (like AX88179) makes development easier.

FAQ

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