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Power Delivery and the Type-C Revolution

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Keysight Technologies

Power Delivery and the Type-C Revolution

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Author

Brig Asay, Keysight Technologies

Power Delivery and the Type-C Revolution

USB-C cords promise to be all-in-one cables for the next decade thanks, in no small part, to the way this new spec handles electrical power. 

Over the next few years, the ubiquitous USB connector will move from the versions familiar today, called Type-A and Type-B, to a new version called Type-C. This is much more than a mere cosmetic change; widely used connection technologies that include DisplayPort (for video), MHL (for audio and video), and Thunderbolt (for data and video) have all announced they’ll move into the Type-C connector. 

Consumers probably think the consolidation of multiple connector styles into one sounds like a great idea. But there are many other reasons to be excited about the change. Some of the reasons include better usability (yes, a USB connector can be plugged in either way), higher power handling power (up to 100 W), and devices using Type-C can be either a supplier or a consumer of power. Additionally, the Type-C connector is smaller.

Excitement around the Type-C connector has brought visibility to a specification that has been around for many years, but is at the heart of many of Type-C connector’s key features. This technology is the USB power delivery specification. USB, DisplayPort, MHL and Thunderbolt are pushing data rates of up to 20 Gb/sec. The USB power delivery specification only runs at 300 kHz, yet there is as much excitement about it as for the other technologies. The reason for all the excitement is that power delivery is the backbone behind the Type-C revolution.

What is power delivery?

The USB-IF website says, “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.” Given the revolution within Type-C, the power delivery specification becomes increasingly important.

Power delivery resolves cable orientation to establish data bus routing, establishes the “host” and “device” roles between two attached ports, discovers and configures the Vbus pin, configures Vconn, and discovers and configures the optional alternate mode. One example from the USB-IF website shows just how configurable the power is: Battery powered devices implementing Type-C can both charge up from a hub and then give power back temporarily if need be. 

The Type-C connector now has 24 pins. These pins include a CC line (channel configuration), which is a single-ended, BMC encoded, 4b/5b signal used for PD (Power Delivery) negotiation. The CC line is where much of the power delivery testing takes place.

A few details about the concept of the alternate mode: Simply put, it refers to running a technology other than USB 3.1 over the Type-C connector. Not surprisingly, alternate mode really depends on the power delivery technology, because the power delivery technology provides the hand shaking between USB and other technologies such as MHL, DisplayPort and Thunderbolt.

Part of the large interest in power delivery stems from the more complicated Type-C connector. Previously, power negation was simple: The connector could only connect one way, power management was straight forward, and only one technology was ever used on a USB connector. Now, the Type-C connector is much smarter in the management of power. Plus, the device must recognize which way the connector is plugged in. The connection won’t work if the devices think the connector is right side up when it is upside down. The increased complexity means there is a need for more test specifications.

The power delivery specification considers such factors as supply drift and static load response. The specification also looks at high-frequency transients and noise and the programmable rail response. The CC line alone has a whole new level of testing, including eye diagram testing, rise time testing and a CRC check. Some of the other tests on the CC line include fall-time testing, bit rate testing, voltage swing testing and inter-frame gap testing. The CC line also undergoes full protocol testing, along with the monitoring of the CC line to ensure that what is being programmed is what is actually being passed through the line. 

 

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