USB Type-C for mobile phones: Changing the way phones connect, one flip at a time


Will mobile phone designers adopt all of the available features in the universal serial bus (USB) Type-CTM specification? Probably not. They’ll weigh their options against the impact on overall product cost. The new USB Type-C interface comes with ultra-thin connectors that are less than 3mm high and 8.4mm wide, making it ideal for mobile phones. USB Type-C offers a cable-and-plug assembly that is “flippable” and reversible. The interface provides options for data and video up to 20Gbps and power up to 100W.

Figure 1: USB Type-C full-featured cable

The USB Type-C interface supports USB 2.0 and 3.1 data and 15W (5V, 3A) power charging natively using a channel configuration (CC) function. The optional USB Power Delivery (USB PD) function enables video such as DisplayPort and power charging up to 100W (20V, 5A).

While USB On-The-Go (OTG) allows mobile phones to assume dual data roles – a host or a client device – USB Type-C introduces a mode called dual role port (DRP) that allows it to have dual roles for both data and power. DRP means that the port can either assume the downstream facing port (DFP) role as the USB host and power provider or the upstream facing port (UFP) role as the USB device and power consumer. As a result, a mobile phone with DRP can get power for charging when connected to a laptop or in turn provide power to a flash drive. USB PD further enables independent data and power roles so that an upstream data port can provide power and a downstream data port can sink power.

As I mentioned earlier, engineers must decide if different USB Type-C features are worth the trade-offs and potential increased cost. Some of the trade-offs may include:

  • DRP versus UFP. While most mobile platforms will implement DRP, some might stick to only UFP for a simpler implementation.
  • USB 2.0 versus USB 3.1. A typical USB 2.0 implementation will have both D+ shorted and D- shorted as stubbed connections, eliminating the need for a multiplexer (mux). Choosing USB 3.1 will require a mux to accommodate USB Type-C cable/plug flipping. For a mobile phone, USB 2.0’s data-transfer rate (-about 40MBytes per second of effective throughput) may be adequate for everyday use.
  • Alternate mode video. Apart from system support for video, a port also requires a USB PD device and a complex data mux such as a cross-point switch, increasing cost. Depending on the system design, additional signal conditioners could also be necessary.
  • 15W versus enhanced power. Native 15W power is part of the USB Type-C CC function and will not require any extra device; however, increasing power capability will require a USB PD device, adding cost. A typical smartphone has about a 6Wh battery and will take around 30 minutes to charge using native USB Type-C. A “phablet” may take about 50 minutes. This speed is six times quicker than standard USB 2.0 charging and 1.5 times than the fastest USB Battery Charging (BC) 1.2 rate.

See Table 1 for USB Type-C options for system implementations.

Table 1: USB Type-C options with a native CC controller versus USB-PD

 

TI’s TUSB320 is a single-chip CC controller solution for mobile phones with USB 2.0 data and 15W of power support. The device provides optional features such as Try.SNK, audio/debug accessory detection, dead battery support and ID emulation for flexible system implementations. Note that two DRPs connected together result in a random power provider/consumer relationship unless the phone becomes a power consumer using the Try.SNK feature. The Try.SNK feature could be useful to avoid situations where a phone starts charging a notebook.

If you are in need of a solution that supports both power and data requirements, TI’s TUSB321 and HD3SS3212 together can provide a USB Type-C solution that provides USB 3.1 for data and 15W for power. The TUSB321 is a CC controller with VCONN power output (required per USB Type-C specs) to support active cables. The HD3SS3212 is a USB SuperSpeed mux supporting USB 3.1 Gen 1 and 2.

TI’s TUSB320TUSB321 and HD3SS3212 meets USB Type-C Specification 1.1 Engineering Change Notices as of June 22, 2015. In addition, we’re early leaders in interoperability, providing the most robust solution for the USB Type-C ecosystem.

What would you like to know about USB Type-C in future blog posts? Let me know by leaving a comment below.

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