The Power Delivery 2.0 Protocol in Action

Figure 1: A high-level view of a PD 2.0 power
contract negotiation

The Power Delivery 2.0 protocol brings a boatload of intelligence to the process of establishing power relationships between partners in a USB Type-C link. In previous posts, we've examined the basics of the two standards, the workings of USB Type-C cable detection, how dual-role port devices are handled, and PD 2.0 messaging. Next, let's look at PD 2.0 in action by deconstructing the initialization of a Google Chromebook laptop, which was one of the first Power Delivery devices on the market.

USB Type-C Cable Detection

Figure 1: The four possible states of
connection for a USB Type-C cable

Having examined some of the basics regarding the USB Type-C connector and the Power Delivery 2.0 specification that complements the Type-C spec itself, we'll turn our attention to the topic of cable detection. The Type-C connector is reversible, which is to say there are four ways a cable can be connected between upstream- and downstream-facing ports (Figure 1). Not only that, but there are different types of Type-C cables. So how do the devices discern what's between them?

A Look at USB Type-C and Power Delivery

Figure 1: The USB Type-C
connector alongside its
Micro-B counterpart

With USB 3.1, the latest iteration of the serial-data protocol, comes a new smaller and universal connector: USB Type-C, the USB-IF's answer to Apple's Lightning connector (Figure 1). Even Apple itself has adopted USB Type-C for its latest MacBooks, a rare show of support from Cupertino for an open standard. Like Lightning, USB Type-C is reversible, but it offers other interesting features, such as the ability to handle other protocols using "alternate modes." It also incorporates the new USB Power Delivery specification for improved power-supply capabilities over USB.