Overcoming Test Challenges of USB Type-C

Authored by Brian Fetz, Senior Marketing Program Manager

The new USB Type-C connector supports attractive features including low profile, high-speed data transport, orientation independence, sophisticated power management capability and high-charging current capability. The combined feature offering has increased the connector’s use for devices in mobile applications such as mobile phones and tablets, as well as, desktop products and consumer electronics.

Engineers who are designing the Type-C connector into their devices face new test challenges that require unique tools and techniques to address the many test parameters and evolving standards associated with the connectors’ expanded capabilities.

This article introduces the USB Type-C connector, the functionality it provides, and new tools and techniques to successfully address USB Type-C product validation.

The USB Type-C environment provides more functionality for data transmission and power options. (Figure 1.)The 24-pin connector can be rotated 180 degrees and still connect to like pins due to its symmetrical pin configuration, making it ‘orientation independent’ or easy to plug in any direction. A closer look at the USB Type-C connectors’ design and individual pins, will help to demonstrate the full potential of its capability as well as its complexity for the test.

High-Speed Data

There are two ports(1&2) in the USB Type-C connector each having two differential high-speed lanes.  In USB3.1 these are transmitted/receive pairs and only one port is active at a time(Figure 1. Ports identified in blue and green) In other applications these ports can be configured to all transmit, all receive, or have one port with a USB3.1 link and the other port with an alt mode link. USB 3.1 data rates of 10 Gbs and TBT3 data rates of 20Gbs has been achieved.  This slim, flippable Type-C connector was designed with a future as 40 Gbsis within reach for a two-lane operation(for a future version of USB for example), or 80Gbs composite in one direction being possible, say for a future version of DisplayPort.

In addition to the high-speed transmission RX/TX pair, the connector includes a simultaneous link of USB 2 (D+, D-) which can be used for standard USB 2 operations or as a supplemental link providing information for power delivery. The D+ connections are tied together, as are the D- connections to maintain the orientation independence of the connector.

Alternate Modes

Alternate modes or “guest protocols” use the transmit/receive (Tx/Rx) pairs for DisplayPort, MHL or Thunderbolt data transfers making it possible to transfer high-speed data, video and audio signals in addition to USB. The alternate modes are negotiated over the power delivery channel and when in such a mode t the SBU1 and SBU2 pins(sideband use) lines are used for control purposes as defined in those standards.

Power delivery

The power pins, four for V_BUSand four for GND provide up to 5 amps and 100 watts for dynamic power and charging of different devices. The power delivery state, including voltage and current levels, and whether provider or consumer, are determined using a protocol over a channel on the CC1/CC2pins.

Cable orientation and dynamic configuration

The CC1 and CC2 lines manage the definition of the connector interface by providing three functions; orientation configuration management, power provision to the cableand communication channel for power delivery. CC1 and CC2 pins are used to establish connectivity between a host and device regardless of the orientation of the cable. The USB Type-C connector maintains a host-to-device logical relationship even though it is reversible using a single-wire orientation detection. When the cable is plugged into the receptacle, the wire connects only one of the CC lines of the receptacle to either CC1 or CC2 on the other end, which determines the cable orientation.

With an understanding of the connectors’ pin functions, we can begin to identify the areas where additional tests, instruments and test fixtures are needed.

USB Type-C test implications

Multiple data protocols and data rates, various power levels with reversible direction and a reversible, flippablecable are all contributors to the need for additional USB Type-C tests. Understanding the key areas of USB Type-C test can help engineers to prioritize and develop a successful test plan.

Key USB Type-C test areas include:

• Ability to control CC1/2 signal loading (R_P, R_D, and R_A) for power-up, debug and test
• Ability to communicate over CC line for:
  • Power setup: V_BUS as consumer/provider, voltage and current settings
  • Alternate mode (protocol) control
  • Dynamic “host” and “device” determination (part of Power Delivery) for dual role ports

• Ability to test the Power Delivery communication channel, its protocol and the V_BUS profile including high current states.

Debug of the PD protocol is one of the biggest challenge engineers face since it requires access to the CC lines and the V_BUS signal in order to be properly characterized.  USB PD has specified voltage/current (power) levels that devices can select for operation making the ability to test PD levels as devices initialize very important.

• Test of both TX1/RX1 and TX2/RX2 ports

For support of USB 3.1 TX test at up to 10G data rate, 14.5dB channel fixtures, with software integrated Continuous Time Linear Equalizer (CTLE) and Decision Feedback Equalizer (DFE), are needed to create the proper compliance channel.

The USB 3.1 specification requires electrical tests that rely on proper setup and analysis for acceptable results. Spread spectrum clocking (SSC) modulation signal is a required test for USB 3.0 and 3.1 in regards to EMI and will ensure the device is able to transmit an accurate profile acceptable for receiver input. Also, the flippable USB Type-C cable requires the RX/TX process to be executed for both cable orientations.  It is also presumed at this point that there is independence in performance from the power delivery setting: an assumption that needs to be verified.

• Driving SBU1 and SBU2 when an alternate mode is used
  
  The SBU lines are used for control of interface standards other than USB3.1. An example of this is the DisplayPort AUX channel which is used to establish a link in DisplayPort enabled devices as well as initiating test modes.
• Test of all standards that will be transmitted
  
  A number of already established standards have announced the desire to use the USB Type-C connector. If a product, for instance, has the ability to transmit Thunderbolt3, DisplayPort and MHL then it will follow that the compliance regimens for these will be performed.

To address the increased number of tests, more complex test configurations and to ensure USB Type-C devices meet the required USB and Alternate protocol standards, engineers require new test capabilities and tools. When armed with the proper tools and techniques for USB Type-C testing, engineers will progress more quickly towards successful, accurate test results.

USB Type-C test solutions

Design engineers are able to save time and test with confidence in their results when they use quality instruments, fixtures and software developed for USB Type-C test.

Here are some examples:

• For managing power and control lines for Power Delivery a Type-C low-speed signal access and control fixture (N7016A) can support termination requirement, test configuration and connection to a power delivery controller. Easy access to CC1, CC2, Vbus and ground signals allows the breakout of USB 3.1 signals from USB devices for system diagnosis and control. Simulation of upstream or downstream devices and ability to flip the Type-C connection allow a thorough test of the Power Delivery functions.
• For management of the CC1/2 BMC encoded, 300 KHz signal, the N8837A USB-PD Protocol Trigger and Decode software for the Infiniium Series oscilloscope can be used during development for debugging and includes enhanced serial analysis capability for decode, listing window view, software searching and trigger.
• Engineers can view the USB 3.1 Gen1 (8b/10b) and Gen2 (128b/132b) protocols to decode and quickly troubleshoot any protocol issues using N8821A USB 3.1 Gen1/Gen2 protocol trigger and decode software for the Infiniium Series oscilloscopes.The software provides a viewable correlation between waveforms and selected packets and allows engineers to move between the physical and protocol layer information using a time-correlated tracking marker.
• Test Type-C and alternate modes using the N7015A Type-C test fixture provides a breakout fixture with very short, low loss cables. The cables, including four pairs of RX/TX and the D+ and D- lanes, connect directly to an oscilloscope for the best signal integrity. De-embedding models of the fixture are also provided.
• For the automatic execution of USB 3.1 electrical tests, the U7243B TX USB 3.1 compliance test software is available.
• Generate USB 3.1 Gen1/2 sequences using the N5990A Automated compliance and device characterization RX software. Control is provided for SCD1/SCD2/LBPM cycles, TSEQ count, TS1 and TS2 count. LFPS period, tBurst, trepeat, tPWM as well as other easily adjusted parameters.
• Receiver characterization for single and multi-lane devices running up to 16 or 32 Gbs is possible using the M8020A J-Bert. Generate calibrated RX test stress conditions such as SSC, sinusoidal jitter (SJ), random jitter (RJ), de-emphasis, and ISI. Both for 8b/10b and 128v/132b coding is supported. It includes integrated link training hardware and TxEq, noise impairment, variable ISI, and receiver equalizer/eye-opener.