What is USB Type-C?
USB Type-C is a USB specification for a small 24-pin reversible-plug connector for USB devices and USB cabling. It supports 10 Gbps data rates, with a path to 40 Gbps, and can source or sink up to 100 Watts (5 Amps at 20 Volts). In ALT mode it supports DisplayPort, HDMI, MHL, Thunderbolt, and it is possible to support other serial protocols like Ethernet and even PCI Express.
The USB Type-C connectors connect to both hosts and devices, replacing USB Type-B and USB Type-A connectors and cables. And for the first time, both the connector and the cable direction is reversible! The new form factor is much smaller, essentially the size of a micro USB Type B connector.
Simplicity and capability for the consumer; one connector for a number of applications and uses, its high data rates, power management capabilities, its ease of use and small size are driving this to be THE interface for laptops, tablets, desktop PC’s, phones, displays, cameras, storage devices, automobiles, external batteries, music jacks, USB hubs, TV’s, and the list goes on. Think about it, use your phone to drive a room projector and while you are presenting the projector is charging your phone. Only with Type-C is this possible.
But this capability and versatility creates complexity for designers, integrators and validators. USB Type-C is one of the more challenging architectures for digital design engineers due to the extreme rise time of the digital signals it’s meant to carry. This, combined with the small physical size of this high-density reversible connector and much higher power specifications increases the risk that design engineers will encounter unforeseen interoperability issues at the fundamental, physical layer. These issues can be avoided by leveraging measurement tools to adequately debug and characterize the performance and validate designs with industry standard compliance applications.
To learn more about USB Type-C, including insights from one of the industry experts, check out our recent Podcast USB Type-C - EEs Talk Tech #1
Diagram courtesy USB-IF
USB Type-C Design
The USB Type-C connector is small, measuring 8.4 mm x 2.6 mm. There are four differential data lanes on this interface, two pair of Transmit and Receive. They are specified up to a maximum of 20 gigabits per second performance. So, this connector is really able to meet most current needs for data throughput with room to grow as data demand continues to rise in the future.
There are four pins on this interface for USB2, shown in grey below, but only two of these pins go through the Type-C cable. The pins were duplicated to simplify the issue of orientation independence.
There are two pins for sideband use which are utilized for the alternate standards, they're called SBU1 and SBU2. These alternative modes include DisplayPort, Thunderbolt, and MHL.
Then there are two pins for configuration and the power delivery channel. These are the CC1 and CC2 shown in purple in the graphic below. This is a single communication channel where all protocol and power is negotiated to create a contract between the host and device. The CC pins have three functions; termination/orientation detection, Vconn Supply, and Power Delivery Channel. The Vconn wire (one of the CC channels) is used to power active or electronically marked cables. When a connection is made the host initiates communication on the CC lines and provides a list of its capabilities such as power levels, display modes, maximum data rate, thunderbolt, etc. The device then indicates its capabilities and the two end points agree on a contract.
Finally, we have four pins for Power called the VBus and four pins for ground, and they're located on the diagram below in red and black. Since there are four of each, this increases the power levels allowed fourfold. This interface allows for VBus up to 20 volts and current levels all the way up to five amps. That means this interface can carry 100 watts of power! This alone is a major concern as many devices will be fried if the power negotiations are not done correctly and accurately.
Type-C Connector Summary:
RX/TX Lanes: 4 High-speed differential data lanes, each specified up to 20 Gbps
CC Lines: Configuration Channel and Vconn Supply
Vbus and GND: The Power Pins. There are 4 Grounds and 4 Supply Pins that handle up to 20 volts and a maximum of 5 amps.
SBU Lines: Sideband Use Pins are extra lines for alternative use.
D+/- Lines: USB2.0 operation and link communication
USB Test Implications
Since D+ and D- are USB2, they are assumed to be active in a Type-C design. Therefore, a full regiment of USB2 test and validation of the device is required in addition to testing Type-C USB3.1. USB2 runs at 480 Mbps in a half-duplex mode where both protocol and PHY level testing is required.
The configuration pins – CC1 and CC2 have a number of different functions. First, they can determine whether a device is connected. They can also determine connector orientation thanks to a termination aspect related to the CC pin. The power delivery channel can be configured with these pins to ensure compatibility between the two devices. Since there are two of these CC pins and only one is connected through to the link, the other may be used to supply power to the cable (Vconn), should it need it.
So what are the test implications for the CC pins? First, there's power delivery channel testing, which means you need to be able to monitor the data coming through that CC pin. You also may need to test with Vconn loaded or unloaded. Because your device may need to power the cable, you must be able to terminate the device you're going to test. In addition, there are serious implications if your power exceeds the proper levels. An incorrect power level could destroy a device, or it could become a safety issue with life threating consequences. Either way, extensive testing and validation is mandatory. The key test requirements for you to consider include protocol and PHY testing for a wide range of voltages and currents as both the provider and the consumer of the power.
In the case of USB3 testing, you must test both TX1 and TX2 ports, which will require doubling the test time. You can either do this testing either by taking out the connector and flipping it over and sticking it back in, or you can do an electronic flip. And if you’re testing Thunderbolt 3 over Type-C you will need to know that all four lanes can be TX or RX.
There are even narrower margins when dealing with 10 or 20 gigabits per second data since the eye height and width are decreased significantly. Since you are concerned about losses in the path, you must ensure you do not have to much loss in the path to your measurement equipment.
Finally, there is testing Type-C alternative modes. You will need to control the CC line to get into the required alternate mode. Testing the configuration channel is very important, not only do you need to verify it, but you also have to use it to control states of your device.
Type-C incorporates many protocols, very high data rates, power delivery, and of course USB2, and the number of signal to observe and control present a number of challenges for testing. The good news is that Keysight’s oscilloscopes can help you test and validate your Type-C device with our full range of protocol and physical layer test and compliance applications.
Keysight’s Type-C test and validation solutions with oscilloscopes:
USB 3.1 Compliance Application – for Gen 1 (5 Gbps) and Gen 2 (10 Gbps)
Keysight’s U7243B USB 3.1 validation and compliance test software provides a fast and easy way to verify and debug your USB 3.1 products. This software allows you to automatically execute USB 3.1 electrical tests and then displays the results in a flexible report. In addition to the measurement data, the report provides a margin analysis that shows how closely your device passed or failed each test to help you determine the exact signal levels within your design.
USB 3.1 Compliance
Keysight’s N8821A USB 3.1 Gen1/Gen2 protocol trigger and decode application includes a suite of configurable protocol-level searches and software-based triggering specific to USB 3.1. The multi-tab protocol viewer shows you the correlation between the waveforms and the selected packet using a time-correlated tracking marker so you can quickly move between the type-c physical and protocol layer information.
USB 3.1 protocol decode with precise time-correlation between waveforms and listing
USB PD Protocol Compliance Software
Keysight’s N8840A USB power delivery (PD) electrical and protocol compliance test software helps you quickly validate and debug your USB power delivery provider, consumer, dual-role device, and eMarker cable. USB power delivery compliance test software allows you to automatically execute a USB Type-C power delivery compliance test plan and then see the results in a comprehensive report (.pdf, .csv, and .xml). These tests conform to the latest USB-IF USB PD specification and test plan and perform electrical physical layer BMC-PHY tests, protocol layer BMC-PROT tests, and power state BMC-POW tests.
USB PD Compliance
USB PD Triggering and Decode
You can extend your oscilloscope’s capability with the N8837A USB-PD protocol triggering and decode application which makes it easy to debug and test designs that include USB-PD protocols using a Keysight Infiniium oscilloscope. This application can set up your USB-PD protocol decode in less than 30 seconds and access a rich set of integrated protocol-level triggers. You can save time and eliminate errors by viewing time-correlated packets at the protocol level and quickly troubleshoot serial protocol problems by identifying their timing or signal integrity root cause.
USB-PD protocol decode with precise time-correlation between waveforms and listing
In summary, it is critical to validate your design to industry specifications to ensure safety as well as device interoperability for new Type-C designs. Keysight’s oscilloscopes can help you achieve your testing goals and help to get your product to market faster.