(Source: So Pooney/stock.adobe.com; generated with AI)
From around 1960 to the beginning of the 21st century, nearly every lower-voltage consumer-electronics device came with a custom AC/DC adapter and charger, usually fitted with a coaxial (barrel) connector. These were used to run the device directly from the AC line (adapter mode) or to charge the device’s batteries.
These chargers were unsophisticated, poorly regulated AC/DC converters that simply pumped current into the battery they were charging or the device they were powering. Control of the charging current and power levels, if any, was the responsibility of the unit receiving power.
Not only did each set of adapters and chargers have different ratings for voltage output and maximum current, but they also used DC connectors of different sizes (Figure 1). These different-sized connectors were meant to “key” the output voltage to the product, preventing mismatches and subsequent overvoltage.
Figure 1: These coaxial (barrel) connectors, with just slightly different inner- and outer-diameter sizes, were used for AC/DC chargers in countless products; they often frustrated users due to their single-use unique compatibility with their associated product. (Source: Rainer Knäpper, Free Art License)
A typical consumer would soon have a drawer filled with a dozen or more of these units, each different and incompatible with other devices. Even well-intentioned efforts by ambitious individuals to instill some order in the chaos by organizing that drawer’s random collection were futile, as the adapter/charger for Product A would be unusable with unrelated Product B. The entire world of AC/DC adapter/charger units was one of incompatibility and user frustration.
This situation changed with the introduction of the original low-voltage Universal Serial Bus (USB) port, initially used for charging smartphones using one of several connector options. The industry soon settled on just a few of these USB connectors, such as USB Type-A and the Lightning connector (a proprietary, 8-pin, reversible connector developed by Apple in 2012 for its mobile devices, including iPhones, iPads, and AirPods).
However, the entire charging landscape has changed dramatically in the past few years. The Common Charger Directive is a European Union (EU) regulation that requires most new portable electronics, including phones, tablets, and cameras, sold in the EU to use a USB Type-C connector (Figure 2) for wired power and charging as of December 2024.[1] The directive created worldwide market pressure to adopt USB-C chargers to minimize waste, advance power-pack reuse, save money, and promote interoperability.
Figure 2: The EU has mandated the USB Type-C connector for charging and powering devices at up to 240W (48V at 5A). (Source: Achira22/stock.adobe.com)
As a result, USB-C has become the dominant wired charging connector for smartphones and many other consumer products. Where USB-C or USB Power Delivery (USB-PD) is implemented, it enables interoperable power delivery across a wide range of devices and power levels. USB-C connectors feature 24 contact pins with carefully defined roles (Table 1).
Table 1: USB Type-C receptacle pinout
GND
TX1+
TX1–
VBUS
CC1
D+
D–
SBU1
RX2–
RX2+
RX1+
RX1–
SBU2
CC2
TX2–
TX2+
As a result, the charger is no longer a relatively passive source that delivers current to a load via the USB-C connector. Instead, it must negotiate, decide, and protect the power link. USB-PD defines normative voltages such as 5V, 9V, 15V, and 20V. In USB-PD 3.1 Extended Power Range (EPR), additional fixed levels exist: 28V and 36V in addition to 48V, which supports power up to 240W.
The behavior and capabilities of a USB-C power source are defined by formal standards rather than by individual vendor implementations. USB-PD ensures that voltage and power delivery are standardized and predictable. Key features include:
Designers of USB-PD units must ensure designs will work with any suitable USB-C load. The USB-PD unit’s design must take into account that it and the loads it supports will be subject to casual use and even abuse over a lifetime of several years. Yet it must also be flexible to adapt to the likely evolution of USB-PD specifications.
USB-PD systems must acknowledge and support three critical architectural issues:
The circuitry needed to implement the solutions to these challenges is embedded in the Nexperia NEX52041, a USB Type-C and PD controller that resides between the AC/DC power stage and the physical USB-C connector (Figure 3).
Figure 3: The Nexperia NEX52041 USB Type-C and PD controller provides the critical protocol and management functions needed for USB-C implementation. (Source: Nexperia)
Among its many features, the NEX52041 supports both USB PD communication over the Configuration Channel (CC) pins and legacy fast-charging negotiation over D+/D−.
It is also designed for power-source applications that support USB-C CC detection, with two dedicated pins (CC1/CC2) that manage USB-PD connections, cable orientation, and supporting power negotiation. These pins allow devices to detect plug-in events, determine power roles (source/sink), and negotiate power levels up to 100W when a 5A-capable e-marked cable is present. The pins prevent damage by ensuring power is not applied until a valid connection is detected—quite a difference from the traditional “dumb” charger/power unit.
Due to the high level of integration and sophistication of the NEX52041, far fewer individual ICs and discrete devices are needed. This results in a system design with fewer uncertainties and interdependencies that need to be checked and validated. Using the NEX52041 in a USB-PD design positions the unit to support a wide range of applications, such as consumer-electronics adapters and accessory devices.
When a USB-C connection is attached, USB-PD negotiation occurs between the source and sink devices. This negotiation establishes PD arrangement and enables the assessment of power delivery modes and values, both of which depend on the load requirements and what the USB source can deliver. As part of this negotiation process, the controller must first determine the cable orientation, as the USB-C connector can be inserted either way, and pin assignments are not known in advance.
The overall PD negotiation process is complex but entirely invisible to the user. It uses a complex back-and-forth sequence to establish a sharing contract. At a high level, this negotiation follows a predictable sequence of steps.
There are four broad steps in the negotiation phase:
If an agreement is reached, the link then proceeds to the actual power-delivery phase, where:
Not all devices that are charged or powered by a USB-C PD connector are compatible with the latest advanced specification. Some predate it and rely on the USB source for simple charging and connectivity.
The latest specification addresses this in older standards by signaling power negotiation over the legacy D+/D– USB data lines. This type of signaling identifies charger types rather than using the primary method for modern USB-C PD, which is the CC1/CC2 lines for high-power negotiation. It also acknowledges real-world connectivity concerns. These concerns include hot-plugging (i.e., connector insertion/removal with the power on), cable failures, mis-negotiation and failure to complete negotiation, built-in overvoltage and undervoltage protection, and tolerance up to 30V on connector pins (unique to the Nexperia NEX52041).
As protection moves from a board-level add-on to the controller itself, important design implications arise. These include a simplified bill of materials (BOM), a cleaner end-product layout with fewer design paths that need validation, and broader device compatibility.
There are more issues, though. With legacy chargers/power units, current and power could flow only from source to load. Now, many connected devices and applications require bidirectional current and power. For example, smartphone power banks need to be charged but must also deliver power to the smartphone; the same requirements apply to other accessories with internal batteries. The USB-C PD protocol handles these situations as well as the inevitable dead-battery scenario.
Static standards can be successful, but a standard that allows for change and enhancements is important in today’s fast-evolving world. For this reason, USB-PD controllers include a provision for programmable memory to allow additions to the basic PD standard as needed, as well as for tailoring it to vendor-specific needs and behaviors. This programmability extends the longevity of the hardware platform and reduces the need for redesign cycles.
Another area of USB-PD extension recognizes the increased use of multi-port USB-C chargers, where a single USB-PD device supports multiple independent loads (such as one or more smartphones, a smartwatch, and a power bank). Providing the needed multi-port power-sharing system requires sophisticated coordination rather than simplistic duplication.
To support these requirements, the Nexperia NEX52041 includes both an I²C interface for inter-controller communication and an embedded microcontroller with 16kB of multiple-time programmable (MTP) non-volatile memory. This allows designers to incorporate algorithms for dynamic power distribution and smarter power allocation without an external microcontroller.
To support engineers’ efforts to use the NEX52041, Nexperia offers a reference design board for a single USB-C PD charger (Figure 4).
Figure 4: The NEX52041 reference design board is a full-featured tool for connecting and evaluating all aspects of the NEX52041 IC. (Source: Nexperia)
The output of this reference design board is a USB-C port, and it uses a decoy to adjust the output voltages. In addition to the NEX52041, the reference design includes Nexperia’s NEX80605 high-frequency resonant-flyback controller and NEX81812 adaptive synchronous-rectifier controller, as well as a 650V GaN HEMT, 100V MOSFET, and 30V MOSFET.
A USB connector is no longer just a “slightly smart” port for charging or powering attached devices and establishing a data link. The connector now has a dynamic, smart, system-level role where the controller does much more than just provide basic protocol setup and protect against power, line, or mishandling problems. An IC such as the Nexperia NEX52041 is a critical element for implementing the advanced decision-making layer between the AC/DC power-source stage and the connector.
Bill Schweber is a contributing writer for Mouser Electronics and an electronics engineer who has written three textbooks on electronic communications systems, as well as hundreds of technical articles, opinion columns, and product features. In past roles, he worked as a technical website manager for multiple topic-specific sites for EE Times, as well as both the Executive Editor and Analog Editor at EDN.
At Analog Devices, Inc. (a leading vendor of analog and mixed-signal ICs), Bill was in marketing communications (public relations); as a result, he has been on both sides of the technical PR function, presenting company products, stories, and messages to the media and also as the recipient of these.
Prior to the MarCom role at Analog Devices, Bill was associate editor of their respected technical journal, and also worked in their product marketing and applications engineering groups. Before those roles, Bill was at Instron Corp., doing hands-on analog- and power-circuit design and systems integration for materials-testing machine controls.
He has an MSEE (Univ. of Mass) and BSEE (Columbia Univ.), is a Registered Professional Engineer, and holds an Advanced Class amateur radio license. Bill has also planned, written, and presented online courses on a variety of engineering topics, including MOSFET basics, ADC selection, and driving LEDs.
[1] https://commission.europa.eu/news-and-media/news/eu-common-charger-rules-power-all-your-devices-single-charger-2024-12-28_en
Nexperia, headquartered in the Netherlands, is a global semiconductor company with a rich European history and over 12,500 employees across Europe, Asia, and the United States. As a leading expert in the development and production of essential semiconductors, Nexperia’s components enable the basic functionality of virtually every electronic design in the world – from automotive and industrial to mobile and consumer applications.
The company serves a global customer base, shipping more than 100 billion products annually. These products are recognized as benchmarks in efficiency – in process, size, power, and performance. Nexperia's commitment to innovation, efficiency, and stringent industry requirements is evident in its extensive IP portfolio, its expanding product range, and its certification to IATF 16949, ISO 9001, ISO 14001 and ISO 45001 standards.