How to Ensure Interoperability and Compliance of USB Type-C Cables and Connectors
Applikationsberichte
This application note is one in a series of five covering the challenges and solutions for USB Type-C design and test.
- cable and connector
- power delivery
- transmit/receive
- simulation-measurement correlation
- Alternate Mode (ALT) (DisplayPort, Thunderbolt, MHL)
Overview
USB Type-C® is a breakthrough standard designed to meet the demand for technology that supports new, ever smaller, and thinner computers and devices, higher-speed data, and more power and flexibility. Key USB Type-C areas of focus include the connection between devices, managing power, and ensuring valid data transmissions. The USB Type-C connection provides:
- Dynamic power and transmission of USB 2.0 with other protocols
- Key interface for many new and future devices
- Backward compatibility
- Reversibility enables ease-of-use
Design and test engineers face several challenges as they integrate USB Type-C into their products while ensuring interoperability and test compliance. Because USB Type-C compliance test standards have increased and become more complex due to higher data transmission speeds, more power, and additional functionality, successful testing requires highly accurate and standard-compliant test instruments, software, and fixtures.
Table of Contents
Type-C Cable and Connectors
Pin functionality overview
USB Type-C cable and connector test challenges
Managing EMI and RFI levels from the cable assembly
Removing test fixture effects
Effects on the channel response
Cable/connector measurement solutions
Recommended configuration
Type-C Cable and Connectors
Several variations of USB cables are used to connect and power devices: Type-A, Type-B, Micro, Mini, and others.
Design and test engineers face several challenges as they update their device interface from 4-pin USB standard A/B connectors to the 24-pin USB Type-C connector. The new USB Type-C receptacle and cable (also called channel) include design changes that address issues with standard A/B type connectors/cables and offer more features and capabilities for new Type-C enabled products. Understanding test challenges and solutions can help ensure successful USB Type-C integration and test for devices.
The USB Type-C cable and connector (the channel) provides not only backward USB compatibility but also increased functionality for power management and data transmission. USB Type-C power delivery provides up to 20 volts, 5 amps, and 100 watts for dynamic power and charging of different devices. The transmit/receive (Tx/Rx) pairs can be used for USB or “guest protocols” such as DisplayPort, MHL, or Thunderbolt data transfer, making it possible to transfer high-speed data, video, and audio signals in addition to USB. Type-C data transfer rates are up to 40 Gbps (USB 4.0 Gen3 and Thunderbolt-3 Gen3), with the ability to achieve 80 Gbps in the future. These new capabilities create a greater challenge for design and test engineers who are working to ensure the interoperability of their USB channel and devices by performing USB-IF standard conformance tests.
Previously, the USB connection consisted of power and two data lines, but the USB Type-C channel can dynamically change power levels and data signals. When the initial end-to-end USB Type-C connection is made, cable orientation is resolved using CC1/CC2 pins (Configuration Channel), and devices acknowledge the connection and establish host/device roles. Then, the power delivery circuit begins to manage power to each connected device through Vbus and Gnd connections. Individual devices determine which of the Tx/Rx pins (and SBU1/2 pins for alternate protocols) are used. The Tx/Rx pins may be used for USB or other protocols, and pins can be combined in parallel for faster data transfers. Channel power and signal levels are managed by the power delivery circuit and can change while a device is connected for charging or new transmissions.
USB Type-C cable and connector test challenges
USB Type-C cable and connector test challenges result from a large number of specifications and backward compatibility requirements. However, meeting these tough specifications is critical because it ensures the successful interoperation of USB products.
According to the USB-IF, previous versions of USB specification signals (USB 2.0 and USB 3.2) must be supported by Type-C. Along with this required backward compatibility, the USB-IF has defined the following USB Type-C cables, both with Type-C plugs at each end:
- The full-featured Type-C cable with a full-featured Type-C plug at both ends for USB 3.2, USB 4.0, and full-featured applications.
- USB 2.0 Type-C cable with a USB 2.0 Type-C plug at both ends (typically for mobile charging).
- Captive cable with either a USB full-featured Type-C plug or USB 2.0 Type-C plus at one end.
- USB3.2 active cable.
Rather than specified cable lengths for electrical compliance channels, USB 3.2, USB 4.0, and USB Type-C have specified channel loss, which plays a key role in ensuring the interoperability of USB hosts and devices. An example would be a two-meter cable which is required to have no more than 7 dB of insertion loss. With a 20 dB SuperSpeed Gen 1 limit, only 13 dB are remaining to split between the host and device.