USB 3.2 and Power Delivery: Insights from USB Developer Days 2017

Eric Huang

Sep 27, 2017 / 2 min read

We've just returned from an enlightening experience at USB Developers Days in Vancouver, B.C., where the focus was on USB Authentication, USB Power Delivery, and most notably, the advent of USB Type-C.

The World of USB Type-C and Its Many Variants

USB Type-C has ushered in an era of diverse cable types, each serving different purposes. These include:

  • USB 2.0 only cables
  • USB 3.x cables
  • USB cables supporting Alt-Mode like DisplayPort (DP)
  • USB Power Only cables
  • Cables with various power ratings
  • Cables combining Power and USB 3.x
  • Cables for Power plus Alt mode
  • And several others

Understanding USB Power Standards

A critical aspect of USB Type-C is its default power delivery:

  • USB 3.2 offers 5 V at either 900mA or 1,500mA, totaling either 4.5W or 7.5W.
  • USB 2.0 provides 5 V at 500mA, amounting to a total of 2.5W.

With the introduction of USB Power Delivery, the USB IF has outlined two new logos for chargers: a standard Charger and a Fast Charger, each indicating the supported wattage. For example, chargers might be categorized as 15W or 45W.

Specifics of Power Delivery

For a 15W charger, it must support 5 V at a maximum of either 1.5 or 3.0 A, offering up to 15 W of charging power. This standard effectively supersedes the older Battery Charging specification for USB Type-C.

USB Power Delivery becomes particularly relevant for power standards above 15W, allowing for either fixed voltage or programmable power supply. It enables chargers to support up to 5 V and a maximum of 20 A, supplying up to 100W.

Safe Charging and Power Negotiation

To ensure safe charging at higher rates, the USB IF and IEC have developed a system allowing power sources and devices to communicate their capabilities. This involves a double exchange of information to ensure safety before operating at maximum power levels. This communication allows devices like PCs or phones (the Sink) to request more power or inform the power source (the Adapter) of their minimum power requirements.
This feature is particularly useful in scenarios where multiple devices, like a PC, tablet, and phone, are connected to a single hub. The power distribution can be dynamically adjusted based on each device's needs, optimizing for usage or charging.

Insights from Microsoft and Google

Among the most insightful sessions were those presented by Microsoft and Google, focusing on proper Type-C implementations. After two years of real-world application, they had valuable insights to share. Microsoft emphasized Windows testing, while Google discussed their Pixel Book implementations. Both companies have developed OS features and hardware to prevent damage from power mismatches. In cases where no power negotiation is possible, the systems default to the lowest power and voltage settings for safety.

A Humorous Take on USB

To end on a lighter note, Agent K and Mick Posner shared an XKCD comic that humorously encapsulates the USB experience. It's a fitting and entertaining end to a topic that's become so integral to our tech-driven lives.

Assortment of USB cables

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