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What’s the New USB Power Delivery Protocol All About?
Jessica Hopkins

In its early days, the Universal Serial Bus protocol, commonly known as USB, was initially created and used as a vessel to power on and transfer data from one device to another. Initially many USB devices on the market required an external power adapter, and over time this proved to be costly and inefficient for manufacturers and users. The increasing need for a common source to supply power and efficiently charge devices initiated a new function for the USB cable; the USB interface was updated to offer charging capabilities on small devices that required 2.5 W-4.5 W of power.

A New Cable is Introduced

Today, many devices on the market are becoming increasingly technical, include more components, and require much more power to operate. To meet these new requirements, the USB-IF has introduced a new type of cable that is more advanced, powerful, and versatile than any other cable on the market, called USB Type-C. The Type-C cable comprises a receptacle with 24 pins, is fully reversible, supports USB data, power charging and video, and can handle up to 20 volts and 100w of power.

How is Power Charging Enhanced in Type-C?

Power Delivery (PD) is a protocol built within the structure of USB technology (including USB 2.0 to USB 3.2) of Type-C cables. Type-C offers unique CC lines where PD communication and negotiation can take place between devices, including power sources and power sinks. Once the negotiation has occurred, current and voltage are supplied through the VBUS; any further data transfer occurs on the High speed or SuperSpeed lines and does not interfere with the PD traffic.

What Functions does Power Delivery Have?

Each USB cable provides a charging standard of at least 5V of power, but with the newest Type-C technology, the voltage can go as high as 20V at 5A, which means that USB PD 3.0 can provide up to 100W power!

Because of the increased power capabilities, power management across the peripherals is an essential feature in Power Delivery communication. It allows for a “handshake” between the devices where the power source presents its power supplying capabilities, and the power sink accepts the power it is capable of handling.

If a power source can supply up to 20W of power, but the sink can only handle 10W, the negotiation process will establish this relationship and the source will only supply the lesser amount. Without this negotiation occurring, harmful power levels could be exchanged, causing shortages or overheating.

Bidirectional power allows for sources and sinks to become exchangeable with the power supply roles. Typically, sources are ports that supply power over the VBUS. They usually are considered downstream facing ports, where the USB data flows from the host or hub to the peripheral. A sink is a port that consumes power from the VBUS and normally is a type of device. It is possible for these roles to be swapped, where the source and sink are now performing the opposite function.

For instance, some laptops can operate using a dual role port where it “self-charges” from a local power supply, but it can also become a power source itself, allowing a connected cell phone to be “bus-powered” through a USB cable to gain a charge.

Total Phase Supports Power Delivery

Total Phase offers the USB Power Delivery Analyzer, which allows testers to monitor and capture real-time Power Delivery traffic on the CC1 and CC2 lines between two Type-C devices. While connected, it passes through any USB 2.0 or USB 3.2 signals, and enables capture of PD negotiation for power, USB data roles, and DisplayPort, or other Type-C alternate modes. Using the Data Center Software, users can monitor detailed sink/source charging level negotiation, test the interaction between source and sink, monitor upstream/downstream port data and power role swap, view current and voltage measurements, and much more. The newest release of the Data Center Software offers added support for PD 3.0 that offers extended messages, handling of new messages, and DisplayPort VDM decoding.

Have any questions about using the Power Delivery Analyzer for your project? Feel free to contact us at sales@totalphase.com. You can also request a demonstration for your application.

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