February 8th, 2018

By Lynnette Reese, Editor-in-Chief, Embedded Systems Engineering

USB Type-C™, delivering both power and data, will grow to 5 billion units shipped worldwide by 2021. And with USB Fast Charging, minutes of charging can power devices for hours.

The Universal Serial Bus (USB) standard has expanded to include Fast Charging, which enables charging for minutes to power for hours without generating excessive heat. USB Implementers Forum (USB-IF) is a non-profit organization that was founded by several companies that jointly developed the USB 1.0 specification and, most recently, added Certified USB Fast Chargers to its Compliance and Logo Program. USB has become one of the most widely used and recognized standards in the world. As of December 2017, IHS Markit predicts that more than 5 billion devices will use the USB Type-C™ connector by 2021. Certified USB Fast Chargers present a broad range of easy-to-use charging solutions. As older devices make way for the new, the difficulty in selecting the correct charger can be reduced or eliminated by using Certified USB Fast Chargers, since compliant USB devices that support USB PD 3.0 can detect, negotiate with each other, and provide power at the proper level. Beyond convenience, Certified USB Chargers have the potential to reduce electronic waste as one charger can work with many different compliant devices across several manufacturers’ products.

Certified USB Fast Chargers support the Programmable Power Supply (PPS) feature of the USB PD 3.0 specification. The PPS feature allows programmed changes in voltage and current levels to charge the battery. Programming charging behavior minimizes energy loss through excess heat (See Figure 2). For the best charging profile that reduces energy loss as the battery charges, voltage increases while the charger applies a fixed current. At a predetermined optimum voltage level for the application, the charger changes modes to apply a constant voltage with a gradual decrease in flow until charging is complete. This charging profile reduces energy loss and keeps batteries from overheating, which can reduce the life of a cell. The PPS feature can be set up to provide an optimal charging pattern based on battery chemistry, maximum allowable temperatures, and other factors.

“A major tenet of USB-IF is listening to developers and OEMs that are adopting our specs and using their feedback as necessary to shape revisions or new initiatives to meet industry needs,” said Rahman Ismail, USB-IF CTO. “Certified USB Fast Chargers accommodate international regulations that require better energy management and add a feature benefit [faster charging] that is passed directly to the user.”

Convenience
In the future, Certified USB Fast Chargers would take a lot of the guesswork out of powering various USB devices by operating via established power rules that automatically decide how devices should behave when charging. For instance, if you have a wall charger that is certified for USB Fast Charging and it is rated at 45 W and your compliant device requires 12 V at 3 A (36 W), you will be able to plug it in without concern for finding, reading, and matching voltage and current levels from source to device. Too much current can overheat and reduce battery life. Too little voltage from your AC adapter may cause malfunction or may not power up your device at all. Since your device requires a total of 36 W and your Certified USB Fast Charger can provide up to 45 W, both devices will detect and adjust themselves so that the USB wall charger (i.e., the current source) can provide the correct voltage to the receiving USB device (i.e., the current sink).

“There are tons of chargers available for people to buy, either online or in almost any store, and it’s hard to know which one to choose,” said Jeff Ravencraft, USB-IF President and COO. “Next time you’re shopping for a compliant USB charger, look for the USB-IF certified logos and you’ll know you’re getting a reliable charger that will work with all of your phones, tablets, and other devices.”

In order to take full advantage of USB Fast Charging, all components of a setup (sink, source, cable, charger, etc.) must be compliant with USB Power Delivery 3.0 and PPS. Once it is widely adopted, Certified USB Fast Charging will eliminate the need for consumers to carry a separate charger for their laptop, smartphone, tablet, e-reader, and other devices. Another benefit is that USB Power Delivery 3.0 can also provide many more watts than today’s average USB wall charger, up to 100 W, depending on what the manufacturer chooses to implement. Higher wattage translates to faster charging and a more extensive range of products that can be supported.

Figure 2: USB PD 3.0 includes PPS, or Programmable Power Supply, which allows for programming how charging takes place. As the battery charges, voltage increases while the charger applies a fixed current. At a set voltage level, the charger changes mode to constant voltage, and there is a gradual decrease in current as the battery charges. This type of charging reduces energy loss. The voltage can be adjusted for temperature. (Source: Renesas)

USB Power Delivery 3.0
Presently, conventional USB set-ups can provide up to a 5 V power supply. The USB Power Delivery 3.0 specification increases the power that can be delivered over a compliant USB Type-C™ cable to up to 100 W. It also enables bidirectional power delivery so that the host or the peripheral device can provide power while leaving the USB Type-C™ cable in situ. The specification also offers intelligent and flexible system-level power management, optimizing power management by adjusting to the power requirements of each connected device and allowing devices to negotiate for only the power that they require. Larger peripherals such as hard disk drives, printers, and displays can receive power directly from the same USB Type-C™ cable that provides the data, eliminating the need for both data and power supply cables. Consider an example where a laptop with a power supply delivers both power and data to a monitor via a single USB Type-C™ cable. The opposite scenario is also possible, where a monitor (with a power supply) shares power and data with a lone laptop through a single USB Type-C™ cable. The USB PD 3.0 specification expands functionality and in order to take full advantage of the benefits of Fast Charging, you will need new USB Type-C™ cables and devices that support USB PD 3.0 and PPS. An out-of-the-box, compliant USB Type-C™ cable without USB PD 3.0 support can carry up to three amps of current, whereas a USB Type-C™ cable that supports the USB PD 3.0 specification may carry up to 5 A (see Table 1).

USB Charging and USB performance are separate protocols. USB Power Delivery 3.0 support is not required for a USB Type-C™ host, cable, or device, which means that some USB products may support USB Fast Charging, but may not necessarily also support SuperSpeed USB 10 Gbps (USB 3.1 Gen 2) data communication speeds.

There are previous iterations of USB Power Delivery, however USB-IF strongly encourages developers to only design products that support USB PD 3.0 and to frequently download the specification from the usb.org website to ensure they have the most up-to-date version.

USB Type-C™ Authentication
The Certified USB Charger Initiative is designed to help consumers avoid low-quality, non-compliant USB chargers. The USB Type-C™ Authentication specification, which defines “cryptographic-based authentication for USB Type-C™ chargers and devices” is another tool developed by USB-IF to support this goal.

The protocol is used to confirm the authenticity of a USB device or charger by a USB host system with enough detail to identify product descriptors, capabilities, and certification status.[i]  USB Authentication is an optional security protocol that enables host systems to protect and mitigate risks against non-compliant USB chargers, devices, and cables, or maliciously embedded hardware or software from USB devices attempting to exploit a USB connection. USB Authentication requires new hardware and software and USB-IF expects USB Authentication adoption to grow in 2018.

Devices and Cables
The USB Type-C™ specification defines the form factor and features for cables, connectors, hosts and devices. USB Type-C™ cables and connectors are slender enough for use with mobile phones and yet sturdy for use with tablets, laptops, and displays. A USB Type-C™ cable’s plug orientation and the cable direction are both reversible, so there is no such thing as an upside-down connector or a wrong connector end to plug in, since both are interchangeable.

The market may experience some confusion as older USB devices and cables are phased out. In the meantime, there are many cable adapters that provide a transition between old and new USB, with old speeds and power capability determining overall system performance. Although many consumers understand that they need an adapter cable to connect a new USB Type-C™ device to an older USB port, they may not always know that the performance is dictated by the oldest device. In order to experience the Fast Charging benefits of USB Power Delivery 3.0 and PPS, an entire setup (host, device and cable/charger) must support the appropriate specifications.

The consumer can manage expectations by looking for products featuring the Certified USB Fast Charger Logo. According to USB-IF, “The new, Certified USB Charger logo represents compliant USB products that have passed USB-IF certification. It also displays and identifies the charger’s capability in watts.” The organization anticipates that the most common power levels offered in new Certified USB Fast Chargers will be at 15, 27, 45, and 60 watts. Certified USB Fast Chargers are just one part of the USB-IF Logo and Compliance Program, which includes trademarked logos and icons for products and packaging to identify performance and charging capabilities.

The USB story is far from over. The complexity of USB has increased, and with it, manufacturer mistakes can happen if the USB-IF specifications are not implemented correctly. USB-IF certification means that products meet USB specifications, comply with the highest USB standards, and have undergone interoperability testing for acceptable operation with other USB products. Consumers are encouraged to purchase USB-IF certified products from trusted manufacturers and to look for the USB-IF Certified Logos on packaging and products.

USB Type-C™ and USB-C™ are trademarks of USB Implementers Forum.

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Lynnette Reese is Editor-in-Chief, Embedded Intel Solutions and Embedded Systems Engineering, and has been working in various roles as an electrical engineer for over two decades. She is interested in open source software and hardware, the maker movement, and in increasing the number of women working in STEM so she has a greater chance of talking about something other than football at the water cooler.

[i] “USB 3.0 Promoter Group Defines Authentication Protocol for USB Type-C™.” BusinessWire, 12 Apr. 2016, www.businesswire.com/news/home/20160412005983/en/USB-3.0-Promoter-Group-Defines-Authentication-Protocol.