The introduction by the USB Implementers’ Forum (UBS-IF) of the most recent version 3.0 of the USB Power Delivery (USB PD) standard promises to spark a new wave of product development. We can expect to see a whole new range of power adapters, power banks, and chargers for consumer devices such as laptop computers, tablets and mobile phones.
USB PD 3.0 over a USB Type-C connector dramatically increases the power rating of the USB interface from a 7.5W maximum to 100W, via a maximum 20V/5A supply. Fast battery charging and the supply of power-hungry systems such as all-in-one PCs over USB Type-C have been made possible by the introduction of USB PD 3.0.
The ratification of the new USB PD 3.0 standard followed the introduction of the USB Type-C interface standard, which provided a new connector/receptacle design. The USB-C plug is reversible, making it more convenient for users. It is also smaller than the familiar USB Type-A connector and capable of carrying HDMI and DisplayPort traffic as well as USB traffic (see Figure 1).
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Fig. 1: The standard USB-C interface can replace multiple other interfaces in consumer devices. (Source: Cypress Semiconductor)
The USB-C connector is also compatible with USB PD 3.0. Now power adapter manufacturers have the potential to produce a power unit or charger that supplies as much as 100W over a small, reversible connector that has a standard form factor and protocol. This means that, in time, it will become familiar to consumers and well understood by them, and should be interoperable with any USB-C device.
It seems like a winning proposition, and indeed analysts suggest that the market for the key controller component in USB PD devices with a USB-C interface is set to grow at a compound annual growth rate of 89% between 2016 and 2021.
Producing a power device that realizes all the benefits outlined above, however, is more challenging than system designers might assume, especially in a compact unit and at a competitive bill-of-materials cost.
First, it might be expected that the existence of the USB-C and USB PD standards would guarantee interoperability between different manufacturers’ products, helping to maintain consumer faith in the USB interface as a channel for charging and powering devices of many kinds. In fact, the USB standard itself and standards which co-exist alongside UBS, such as the Qualcomm Quick Charge technology for fast charging of mobile devices, are subject to regular revisions and updates to take account of emerging user requirements and new technical capabilities. The latest revision of the Quick Charge technology is version 4.0. That means there have already been three major revisions since v1.0 was released – and v4.0 is not likely to be the last.
At the same time, the USB PD 3.0 standard is itself more than a power specification that sets limits for the input voltage and current to a power-consuming device. More of the standard is devoted to the communications protocols by which connected devices establish their identity, the functions which they are capable of performing, and the role they are going to play as either power provider or power consumer in any given session. The standard also includes provisions for programmable power supplies that can produce a variable output power for use with multiple end devices.
In summary, then, the engineer responsible for designing a USB-C power adaptor or charger with USB PD 3.0 capability will often be required to:
achieve conformance to the USB PD 3.0 specifications
provide scope in the design for regular updates to take account of changes in specifications
implement additional features, including a programmable power supply and support for Quick Charge technology.
Drawbacks of discrete implementations
A USB-C PD 3.0 system that can meet the requirements above has certain functional requirements, some of which will be implemented in hardware and some in software.
The hardware functions will include:
a USB PD power controller
voltage regulation to supply the power controller and other active components
a high-voltage P-channel MOSFET, switching power to the powered device in response to PWM signals from the USB PD power controller
a high-voltage gate driver to drive the MOSFET
short-circuit protection on the Configuration Channel (CC), specified in the USB-C standard, which is used to carry PD protocol signals
over-current protection on the input power-supply bus (VBUS )
In software, the power adaptor will need to implement the USB-C and USB PD 3.0 protocols, as well as the Quick Charge protocol, if required.
It is possible to implement these hardware and software functions through the use of multiple discrete components. A typically architecture includes a microcontroller to perform system control and power control functions as well as to run the protocol software, alongside a discrete MOSFET, gate driver, and over-current, over-voltage and ESD protection components.
Implementing a USB-C power adaptor, power bank or charger in this way, through the use of multiple discrete components, has various drawbacks:
high component count
multiple components occupy a relatively large board footprint, making for a larger, more complex and more expensive PCB
a system consisting of multiple fixed-function, hardware components tends to become inflexible over time, making it harder to update the design quickly in response to changes in specifications or user requirements
Integration for simplicity and cost reduction
To address these drawbacks, manufacturers are producing integrated silicon that provides both the functionality required for the USB-PD specification as well as the flexibility to update designs as the specification matures and revisions of co-existing standards arise. Power delivery controllers such as Cypress Semiconductor CCG3PA integrate the required hardware functions, apart from the high-voltage power switch, into a single system-on-chip. Manufacturers of such devices also provide the USB-C, USB PD 3.0 and Quick Charge 4.0 protocol stacks. In the case of the CCG3PA, this software runs on an embedded ARM® Cortex®-M0 processor core.
For flexibility, these SoCs provide sufficient Flash memory with read-while-write capabilities to support firmware upgrades and maintain interoperability. To further speed design, SoCs are certified as conforming to the USB PD 3.0 standard, as well as being compliant with the Quick Charge 4.0, 3.0 and 2.0 specifications.
Figure 2 shows the block diagram of a USB-PD integrated controller. By providing a high level of integration, engineers can leverage the advantages of a reduced component count, reduced board footprint, simpler board layout, and lower bill-of-materials. PCB cost and complexity is also substantially reduced compared to a functionally equivalent system implemented through the use of discrete components. For example, compact system-on-chip controllers for USB PD 3.0 over USB-C require only the addition of an external MOSFET and AC-DC converter to implement a complete offline power adaptor/charger for the latest USB Power Delivery standard.
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Fig. 2: SoC-based USB-PD controllers such as the Cypress CCG3PA shown here provide a high level of integration to simply design and lower design cost and complexity. (Source: Cypress Semiconductor)
These system-level advantages, which apply throughout the production lifespan of the product, are considerable. But there is also an important benefit in the design cycle: integrated controllers are backed by a comprehensive set of development resources. These enables a dramatic reduction in time-to-market compared to a typical development process using discrete components. Resources can include:
Multiple reference designs, accelerating specific designs such as USB-C notebook power adaptors (up to 45W), and mobile device chargers (with a maximum power profile of 27W). Reference designs are backed by documentation, including circuit schematics, that can substantial reduce the learning curve for designers new to the USB-PD standard.
Evaluation kits feature USB-C sink or source ports and potentially USB Type-A source ports. Evaluation kit may be used to power and charge notebook computers, mobile phones and other USB devices, and to charge one- or two-cell USB-C power banks.
Together, reference designs and evaluation boards provide an advanced blueprint for many end product designs, requiring only slight modifications to adapt designs to particular customer requirements. Thus, OEMs can achieve substantially faster time-to-market.
Rushil Kadakia is staff product marketing manager at Cypress. He has an M.S.E.E from the University of Southern California. He works with USB, USB-C and FPGA systems. He can get reached at firstname.lastname@example.org.