Electronic Design
Type-C Connectors Seize Multi-Interface Versatility

Type-C Connectors Seize Multi-Interface Versatility

The USB 3.1 Type-C connector has dominated the USB space, but now it’s branching out toward other platforms such as DisplayPort.

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1. The USB 3.1 Type-C connector is reversible.

Is the VESA USB 3.1 Type-C connector (Fig. 1) the one connector that will rule them all? It may very well be the only connector on host devices like smartphones, tablets, and laptops in the future, with its ability to handle a range of interfaces beyond USB 3.1. It’s also reversible (see “USB 3.1 Type C Connector Is Reversible”) and can carry more power. Of course, with signals running at 10 Gb/s, the USB connection can be a challenge to test (see “Why Is the USB Type C Connector So Testy?”).

2. The 24-pin USB 3.1 connector incorporates multiple interfaces, including a configuration bus.

So, what’s behind this multilingual, “alternate mode” nature of the Type-C connection? To start with, the 24-pin connector (Fig. 2) has multiple communication links, including a USB 2.0 and high-speed serial interface that defaults to USB 3 (it runs independently of the USB 2.0 interface on different pins). In addition, a configuration interface actually controls power and the high-speed path, which is where the connector gets its multiprotocol support.

Essentially, the two devices at either end of the cable negotiate the interface to be used with the high-speed serial connections (Fig. 3). A crossbar switch redirects the high-speed Type-C connections to the appropriate redrivers connected to the host’s I/O hub. The External detection control tackles overall configuration (including determination of the host device, where appropriate) as well as USB power management. A USB 2.x device was limited to 500 mA or 2.5 W, while USB 3.1 handles up to 100 W.

3. A dual protocol interface uses a crossbar switch controlled by the External detection control unit to switch between USB 3.1 and another interface (e.g., DisplayPort).

For now, multichip solutions are the most likely to implement connections that support more than one interface. In the future, though, look for popular platforms to emerge with combinations like USB 3/DisplayPort. These will typically be found on host devices like smartphones, tablets, and laptops, but there are scenarios where alternate-mode operation makes sense. For example, a display device might support DisplayPort, USB 3, and even PCI Express. Consequently, the display could be driven by a host that had only of these interfaces. Devices that support more than two modes will likely be rare, given the added cost and complexity for multiple-interface support.

4. USB 3.1 Type-C sockets come in multiple shapes and sizes.

These small Type-C connections come in various forms to address a range of installations (Fig. 4). Note that the same connector is at both ends of the cable, compared to the typical USB cable with a different connector at each end. It’s built this way for two reasons. First, control, power, and data transfers can start at either end, and have different sources. For example, a device could be a slave but provide power. It allows for scenarios such as connecting a smartphone to a tablet. Second, the approach simplifies cable construction and cable use. There is no wrong way to plug it in.

The Type-C connection is just starting to make an impact on system design and consumer usage patterns. In the end, it may be the one connector that outlasts them all.

Download this article in .PDF format
This file type includes high resolution graphics and schematics when applicable.
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