About two months ago, ST launched the STUSB4500, its first USB-C sink-only controller compatible with Power-Delivery (PD). Sink-only means that it is exclusively for charging purposes, and it comes as a complement to the STUSB4700 that works for source-only devices (chargers) and will help USB-C charging solutions reach critical mass, thanks in part to its impressively small CSP–25 packaging of only 2.6 mm x 2.6 mm. Following the initial announcement, we decided to delve deeper into the technologies that make the STUSB4500 a remarkable device, while also exploring some of the hidden gems that make it one of the most flexible and practical solutions on the market today.
The Victims of the USB’s Success
USB Type-C is by itself a groundbreaking solution in an industry that is trying to rectify a lot of the unforeseen problems that plagued the previous generation of USB connectors. No one predicted the meteoric rise of USB charging in the industry and Micro-B connectors suffer from poor endurance. With only about a thousand plugin-unplugging cycles due to a fragile structure, they don’t have a lifespan compatible with decades of usage by consumers who often have to try two to three times before they can finally insert their plug. Now that USB Type-C is more robust and reversible, the new connectors can last at least ten times longer while offering a much friendlier user experience.
Furthermore, USB Type-C PD can now deliver up to 5 A and 20 V, which means that many manufacturers no longer have to rely on DC barrels, which contribute to people’s cable clutter. By using an open and widely popular interface like USB Type-C, companies help reduce the pollution associated with the proliferation of proprietary cables, and they lower costs since integrating a USB charging system is a lot cheaper. As a result, if we had just implemented the standard protocol, the STUSB4500 would already be a great device as it would help manufacturers transition to a much better system. However, as usual, we decided to include additional features to surpass expectations.
An Independent USB-C Sink-Only Controller
One feature that distinguishes the STUSB4500 from the rest of the industry is its standalone mode. By integrating the entire protocol in the device, designers do not need to rely on a microcontroller (MCU) or additional software to start charging a battery. Engineers can choose to create a more complex system if they would like to cover multiple power profiles and use cases, but it’s not a requirement. They can just set a default configuration that will start charging the battery as soon the system connects to the charger. Multiple safeguards will prevent a transfer of energy if the charger doesn’t meet the default’s requirements, but this is one of the most straightforward USB Type-C PD sink-only controllers today.
Ensuring that the charger meets the proper requirements before letting the current flood the system is particularly important to ensure the safety of the product and the user, which is why we also offer a dead battery mode. Because USB Type-C products can connect to a wide range of chargers, the standard includes a series of electronic checks that make sure a particular source is compatible with the product. However, if the battery is entirely out of juice, it is impossible to power a microcontroller and run these algorithms. The answer comes in the form of the dead battery mode, which consists of an IC that will draw a small amount of energy, regardless of the charger, run the necessary checks, and determine if the device can start charging or if the source is not electrically compatible.
A New Way to Build Power Profiles
Standalone and dead battery modes are possible because engineers can preconfigure and store a default profile that will specify the charger’s characteristics. In fact, we ship the STUSB4500 with the standard 5 V, 15V, and 20 V profiles to ensure that the IC will support the most common sources out of the box. We also offer a Graphical User Interface (GUI), the STSW-STUSB002, so engineers with more expertise can customize their settings to adapt to specific chargers. It is then possible to export them and store them in the controller’s memory. This can be particularly useful to first set a universal 5 V / 3 A profile for regular chargers, and then add a fast charging 15 V profile compatible with most AC adapters as well as a custom 14.5 V / 2.1 A setting to match the electrical characteristics of a specific source.
Once a company certifies its prototype, manufacturers can export their profiles from the GUI and flash them onto the STUSB4500 preset on their production PCB. However, our controller is also unique because it enables the creation of a profile at the factory thanks to a very original pairing system that is activated through an external MCU. Since a lot of manufacturers buy their chargers instead of making it themselves, the USB-C sink-only controller must primarily adapt to its characteristics. As a result, we created a pairing mode for the STUSB4500. When our controller, while in pairing mode, connects to the charger, it captures the source’s electrical profile and immediately records it in memory, thus completely bypassing the need for any further developments and making this a genuinely plug-n-play charging solution.
A Controller That Works for You
One underrated aspect of our new STUSB4500 is that it hastens developments while alleviating the need for an extensive knowledge of USB standards. Someone with absolutely no experience in writing code for a USB charging solution can still pair a product with a charger to get the profiles they need and make the system functional. Additionally, even if a USB certification means a device is electrically compatible with the ecosystem, it isn’t always a guarantee of robustness and perfect safety.
The STUSB4500 is therefore unique because it benefits from the years of experience we gained building power devices. Its integrated voltage monitoring, its dual VBUS gate drivers (one for low voltage, such as 5 V, and one for high voltage, meaning up to 20 V), as well as its impressive temperature range of –40ºC to +105ºC, will give an unparalleled peace of mind to our customers who won’t have to deal with massive malfunctions. The recent stories of USB products breaking down or even exploding shows time and again that choosing a poor controller can quickly lead to a crisis in customer support and an almost irreversible loss of trust from the public.
Where to Start?
To start experimenting with the STUSB4500, developers can get a traditional STEVAL-ISC005V1 evaluation board that comes with the controller, multiple output paths, and a way to connect to the NUCLEO-F072RB. It targets teams that want to test the totality of the component’s features, meaning low and high voltage applications. The board also includes a 5 V DC-DC converter to use a single 20 V supply to power everything, from the USB charging system on the board to an external MCU or a motor. As a result, developers can immediately start building a vast range of prototypes since it contains all they need to get an embedded system of the ground.
Additionally, we are introducing the STREF-SCS001V1, a minimal reference design measuring only 30.5 mm x 11.2 mm and that is compatible with 100 W applications. The idea is to show engineers how they can build simple and compact designs with most of the features that the majority of products will require. To obtain such a small size, we took a minimalistic approach, meaning that it doesn’t have the 5 V DC-DC converter of the largest board and it only uses one output path.