Overcoming Test Challenges of USB Type-C
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, 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 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 transmit/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 be transmit, all receive, or have one port with a USB3.1 link and the other port with a 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 fu-
ture 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 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(side band use) lines are used for control purposes as defined in the those standards.
The power pins, four for VBUSand four for GND provideup 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 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 recep- tacle, 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 areasinclude:
Ability to control CC 1/2 loading (RP, RD,and RA) for power up , debug and test Ability to communicate over CC line for: Power setup:VBUS as consumer/provider, voltage and current settings o Alternate mode (protocol) control o 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 VBUS 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 VBUS 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.
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: as an - sumption that needs to be verifiedas.
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- - - - Authored by BRIAN FETZ, Senior Marketing Program Manager Wireless Devices and Solutions Group Keysight Technologies, Inc