Teardown of a USB-C to 2.5G Ethernet Adapter

NOTE：Click here for the Chinese version.

As modern laptops become increasingly slim and light, especially with the MacBook series becoming mainstream today, the USB-C port has become a standard configuration. However, this has also led to a shortage of ports. Particularly, wired Ethernet ports have almost disappeared on devices pursuing portability, making high-speed, stable network connections a pain point. 2.5G Ethernet, as an upgraded standard from Gigabit Ethernet, can provide higher transmission rates, making it very suitable for large file transfers, NAS access, and high-definition multimedia streaming. Therefore, for this edition, we have chosen to teardown a high-end USB-C to 2.5G Ethernet adapter available on the market.

The product selected for this teardown is a Belkin dock. The main reason is that this company is an Apple-certified accessory brand. Additionally, its price is sufficiently high, with a premium of 100% to 200% compared to similar functional accessory products. Thus, we were very curious whether this product is truly made with quality materials or simply a tax on the uninformed. One particularly interesting point is that this product is actually not made in China, but in Vietnam. Has manufacturing migration already reached a significant scale? However, judging just from the selling price, products manufactured in Vietnam and sold in China are not cheap, and might even be more expensive than locally manufactured ones.

Teardown

During the actual teardown, we found the manufacturing process to be somewhat rough, and the structural design wasn't particularly clever either. Essentially, the outer shell could only be removed by force. Inside, there is a metal shield covering the entire PCB board to reduce electromagnetic interference.

On the other side of the PCB board, there are basically only some passive components, an RJ45 Ethernet port, and a USB-C connector. The USB-C interface features a reinforced design to ensure reliability.

After removing the shield, the hardware scheme of the entire adapter is revealed, which is quite concise and clear.

The functionality of the entire adapter primarily relies on two main chips and other peripheral components.

First is Realtek's Ethernet controller chip, the RTL8156BG, which integrates MAC and PHY, supports 10/100/1000M/2.5G speeds, and uses a QFN package. It enables the USB 3.0 to 2.5G Ethernet application. Next to it is a 25MHz crystal oscillator, providing a precise time reference for the chip.

The other main chip is UDE's (Yude Electronics) network isolation transformer, model L22H017-0. It couples the differential data signals output from the RTL8156BG onto the Ethernet cable and provides functions such as electrical isolation and suppression of common-mode interference, improving signal integrity and reliability.

Furthermore, the PCB board includes some power management circuitry. The main power supply is obtained as 5V from the host's USB-C interface. Internal voltage regulation circuits convert this to the various voltage levels required by the chips. Therefore, the power management circuit includes voltage regulators and various filter capacitors to provide stable, clean operating voltage for the chips.

So, the specific working principle of the adapter is:

Downstream direction (Computer → Network): Data starts from the computer's USB-C interface, transmitted via the USB 3.0 data cable to the Realtek RTL8156BG chip. The chip's internal USB MAC and PHY layers process the data, converting it into a format suitable for Ethernet transmission. The signal is then sent to the UDE L22H017-0 network isolation transformer for signal coupling and isolation, and finally delivered to the RJ45 interface.
Upstream direction (Network → Computer): Differential signals from the network cable enter through the RJ45 interface into the UDE L22H017-0 for isolation and coupling. They are then sent to the Realtek RTL8156BG chip, where the internal Ethernet PHY and MAC layers restore the signals into data. This data is then encapsulated according to the USB interface protocol and transmitted to the computer.

Summary

From the teardown, it's not difficult to see that Belkin's adapter hardware does not "transcend" or stand out as unique. It uses the Realtek RTL8156BG as the main controller chip paired with the UDE L22H017-0 network isolation transformer, which is also the mainstream solution in the current 2.5G USB NIC market. Neither the craftsmanship nor the performance shows obvious justification for the premium price. Therefore, if you have a need for a USB-C to 2.5G Ethernet accessory, perhaps consider paying attention to domestic products – the same solution for less than half the price, isn't that a better deal? So, what are your thoughts on this Belkin product? Feel free to leave a comment and discuss!