Saturday, April 20, 2024

Exploring USB Type-C And USB Power Delivery

Every now and then there is an innovation or advancement that changes the way we operate, the way the world operates. These innovations and advancements in technology create opportunities for businesses and provide improved features to consumers. These are also widely and swiftly adopted. USB Type-C is one such technology advancement that will soon be found in most devices. Apple and Google have taken the lead, whereas companies like Dell and many more are following suit.

USB interface is the most widely-adopted interface specification that is being used across all industries. This interface has slowly eliminated legacy serial and parallel ports. Now with advancements in computing technologies, devices are far more efficient and have reduced form factors. This has necessitated a change in the existing USB connectors.

USB Type-C specification is targeted towards new, compact and power-hungry devices and brings in a new flavour to the USB connector. This new ecosystem is also managed by another new specification, namely, USB Power Delivery (PD) specification, which allows managing power and functionality over the new USB Type-C connector.

This article aims to provide an insight into USB Type-C specification, USB PD specification and new functionalities you shall see and experience with the new USB Type-C ecosystem.

USB Type-C overview
USB Type-C cable and connector specifications cover mechanical, assembly and connection detection and configuration part of the USB Type-C ecosystem.

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Unlike the legacy USB connector that has separate connectors for host and devices, Type-C connector uses the same connector for both host and device. The host and device relationship is negotiated using the configuration channel (CC) signal.

USB Type-C interface can be classified into two major types, namely, USB Type-C receptacle and USB Type-C plug.

USB Type-C receptacle. USB Type-C interface on a host or device is generally a receptacle connector as illustrated in Fig. 1.

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fig 1
Fig. 1: USB Type-C receptacle (Ref: USB Type-C specification)

The receptacle in Fig. 1 provides multiple sets of signals to enable the desired functionality irrespective of the plug orientation. For a full-featured USB Type-C receptacle, all indicated signals are required.

USB Type-C plug. USB Type-C plug interface is a connector that is present in a cable or device like mouse or flash drive with only one CC pin and one set of USB 2.0 lines as shown in Fig. 2. The single CC pin allows orientation detection and the other CC pin of the receptacle is used for sourcing VCONN.

fig 2
Fig. 2: USB Type-C plug (Ref: USB Type-C specification)

It is important to note that the super-speed lines are cross-connected on Tx and Rx in a cable.

Let us now take a brief look at the signal lines on the USB Type-C connector.

Configuration channel pins. CC1/CC2/CC. A CC signal is used to detect connection, orientation and also configure the devices into their operating modes. Based on connection orientation, one of the CC lines acts as VCONN signal to provide power to the other end.

Power pins. VBUS are for USB bus power and can carry up to 20V/5A. These are available only after connection detection.

VCONN are used to provide power to the attached plug and are applied via the unused CC pin based on connection orientation.

Auxiliary pins. SBU1/SBU2. The side-band use (SBU) pins are provided for adding additional functionality either through future USB specification or during alternate mode functionality or as an audio accessory.

USB 2.0 pins. DP/DM. D+ and D- pins are used to support USB 2.0 in all three modes, namely, low speed, full speed and high speed. These pins are provided as pairs in a receptacle to support the plug-flipping feature and are shorted in the plug connector.

Super-speed pins. RXn+/RXn-, TXn+/TXn-. These lines are used to implement Rx and Tx of USB 3.1 super-speed interface. These are shared by other interfaces when in alternate mode.

USB PD specification
Even before the new USB Type-C connector was introduced, USB-IF published USB PD specification, which defines how a USB interface can deliver 20V to its port partner. Version 1.0 of the specification uses BFSK on VBUS line for protocol communication.

Later, with the introduction of USB Type-C interface connector, USB PD specification has moved on from BFSK on VBUS to BMC based protocol communication on the CC signal line. A new specification version 2.0 has been released with the above-mentioned changes allowing USB PD protocol to negotiate higher power with the port partner and also jump to alternate functionalities like Displayport, MHL and others over USB Type-C signals.

A USB Type-C device can be broadly classified into two categories: USB Type-C device and USB Type-C device with PD capability. A standalone USB Type-C device supports up to 5V/3A operations and orientation detection, whereas a USB-Type-C device with PD capability supports up to 20V/5A operation and multiple interfaces using alternate modes.

fig 3
Fig. 3: USB Type-C DFP-UFP connection

USB Type-C host or down stream facing port (DFP) to USB Type-C device or upstream facing port (UFP) connection. When two simple forms of USB Type-C devices, a USB host and a USB device, are connected, a USB host will present an Rp on the CC line and a USB device will present an Rd on the CC line as shown in Fig. 3.


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