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USB Power Delivery

Background

In July 2012 the USB Promoters Group announced the finalization of the USB Power Delivery ("PD") specification, where USB evolves from a data interface capable of supplying limited power to a primary provider of power with a data interface. Today many devices charge or get their power from USB ports contained in laptops, cars, aircraft or even wall sockets. USB has become a ubiquitous power socket for many small devices such as cell phones, MP3 players and other hand-held devices. Users need USB to fulfil their requirements not only in terms of data but also to provide power to, or charge, their devices simply, often without the need to load a driver, in order to carry out “traditional” USB functions.

The USB Power Delivery Specification enables the maximum functionality of USB by providing more flexible power delivery along with data over a single cable. Its aim is to operate with and build on the existing USB ecosystem. "PD aware" USB cables with standard USB type A/B connectors to deliver up to 100W of power at 20V. For PD-aware cables with USB-micro B/AB connectors the maximum power supported is up to 60W at 20V, 36W at 1V and 10W at 5V. The intent is to permit uniformly charging laptops, tablets, USB-powered disks and similarly higher power consumer electronics, as a natural extension of existing European and Chinese mobile telephone charging standards.

Features

USB Power Delivery offers the following features:

  • Increased power levels from existing USB standards up to 100W.

  • Power direction is no longer fixed. This enables the product with the power (Host or Peripheral) to provide the power. 

  • Optimize power management across multiple peripherals by allowing each device to take only the power it requires, and to get more power when required for a given application. 

  • Intelligent and flexible system level management of power via optional hub communication with the PC.

  • Allows low power cases such as headsets to negotiate for only the power they require.

Use Cases

Here are a few typical use-cases for Power Delivery:

  1. Enables new higher power use cases such as USB bus powered Hard Disk Drives (HDDs) and printers. This eliminates the need for a separate power brick.

  2. A monitor with a supply from the wall can power, or charge, a laptop while still displaying.

  3. USB power bricks or chargers are able to supply power through a laptop’s USB ports.

  4. Laptops and USB power bricks can provide higher power to battery powered devices (not currently defined by USB).

  5. Battery powered devices can get increased charging current from a hub and then give it back temporarily when the user’s HDD requires to spin up.

New challenges for developers

USB Power Delivery introduces a new side-band communication over the Vbus wire. Similarly to the power-line technology, PD uses an FSK signal having a carrier at 23.2MHz and delivering a throughput of 300kbps.

This new side-band communication has to be coordinated with the classic USB 2.0 and USB 3.1 communication, adding a level of complexity to developers taking advantage of this increased power.

To enable adopters of this cutting-edge technology, Ellisys creates the most technologically advanced protocol test systems including protocol analysis, traffic generator and compliance verification. The Ellisys USB Explorer 350 is latest and greatest protocol test system for USB Power Delivery. Learn more »

Links

Here are a few links to pages containing a whole information range about USB Power Delivery:

USB PD homepage
USB PD specification

USB PD DevCon presentations
Ellisys USB Explorer 350 Power Delivery Analyzer and Generator

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