The USB-C 20G Loopback Plug

Uchi Embedded Solutions
Jun 30
4 min read

A simple way to test, benchmark, and diagnose USB-C ports — USB4 compatible, up to 20 Gb/s

USB-C ports all look the same from the outside, but they don’t always behave the same. Some run slower than they should. Some quietly drop data. Some work fine for a few minutes and then fail under heavy use. The USB-C 20G Loopback Plug is a small, pocket-sized tool that helps you find these problems fast. Plug it into any USB-C port, run a test, and you get clear answers about speed, errors, power, and cable quality.

The USB-C 20G Loopback Plug — a compact, all-in-one USB-C port tester.

What this tool does

Verify that data moving in and out of a USB port is completely error-free.
Measure the real read and write speed of the port, not just its rated number.
Diagnose faulty ports by showing the exact type of error and how often it happens.

Key specifications at a glance

Maximum speed	Up to 20 Gb/s (USB 3.2 Gen 2x2)
Standard	USB4 compatible
Power Delivery	Reads port profiles; can trigger up to 48 V (EPR)
Tests included	Speed, errors, burn-in, power profiling, and cable checks
Control	Windows application, programmable API, and firmware updates

Speed Benchmarking

This test measures the highest read and write speed a USB port can reach. The device pushes data through as fast as possible and records both the peak and the average speed over time.

It lets you confirm whether a port truly delivers the USB 3.2 Gen 2x2 performance it claims — or quietly falls short of it.

Error Detection

A loopback test sends data out of the port and checks that the very same data comes back. If even a single bit is wrong, the device catches it. Every error is logged with its type and count, so you can clearly see whether a port is fully reliable or is silently dropping data.

This makes it easy to spot weak or failing ports before they cause real problems in the field.

The results log lists each error by type — physical layer, 8b/10b decode, and CRC — with a running count.

Reliability & Burn-In Testing

Some faults only appear after long, heavy use. This test keeps a steady, continuous data load running on the port for an extended period. It helps reveal the intermittent glitches and heat-related issues that a short test would miss — making it the right tool for burn-in testing and for proving that a system stays stable under sustained load.

Read speed traced over a long burn-in run, showing how the port holds up over time.

Port Profiling (Power Delivery)

Using USB Power Delivery (PD), the device can read everything a port advertises — its supported voltages, current limits, and maximum power.

It can also request specific voltage levels, up to 48 V with Extended Power Range (EPR). This lets you test a port across all its power modes, not just the default one.

Cable Detection

USB-C cables vary a lot in what they actually support. Through USB Power Delivery, the device reads a cable’s built-in information: its identity, supported data rates, and power rating.

This tells you at a glance whether a cable is safe for high-speed data and high-power charging — or whether the cable is the reason a setup is underperforming.

Software, API & Firmware

PC Software

The loopback plug comes with a dedicated Windows app. From one clean screen you can set up tests, choose the speed and voltage, and watch the results as live logs or graphs. Any result can be saved for later review.

Setting up a loopback test in the PassMark Windows software.

API Programming Support

An API lets other software talk to the device directly. You can write your own scripts and automate the whole testing process — ideal for a production line or any place where many ports need to be checked at scale.

Updatable Firmware

The firmware can be updated, so the device keeps up with new USB standards and can gain new features over time. That keeps your investment useful for years to come.

Where It’s Used

Manufacturing & QA — high-volume testing of USB ports on the production line to keep quality consistent.

Compliance Testing — confirming that ports meet USB specifications for speed, power, and compatibility.

IT Diagnostics & Repair — quickly checking port health and performance during service or repair work.

The Ports on the Device

The loopback plug has three USB-C connections. Here is what each one does:

The three ports and the optional cables used with the device.

Test Unit Port — the USB-C port you connect to the port being tested. It also powers the device: plug it in and the loopback plug turns on.

External Load Port — adds extra load to the USB line so you can test under real-world conditions. It includes built-in current protection and is controlled from the software.

Debug Port — an optional port for steady power or for connecting a second computer to log results. It can power the device on its own, so you can keep testing even if the main port is faulty or unstable. It also makes cable detection more reliable by removing power on delays.

Pre-Testing the USB-C has Over voltage

Protect your USB-C Loopback plug by pre-testing faulty ports for over voltage with the PassMark USB-C S.O.S Short Circuit Tester.

This durable and simple test plug will provide you with a visual indication port voltage in seconds, saving your USB-C Loopback unit from potential damage. This is especially useful in production line testing.

USB-C S.O.S Short Circuit Tester.

If your USB S.O.S pre-test comes back with a Pass, you can move onto more comprehensive troubleshooting with your USB-C 20G Loopback and accompanying software.