Designing for USB-C Just Got Easier
April 02, 2019
| By: Perry Tsao
Executive Director, Mobile Solutions Business Unit
It doesn’t seem like very long ago when industry analysts were waxing poetic about the transformative nature of USB-C (formerly known as USB Type-C), even while adoption sputtered along. Today, most laptops, phones, and PCs are built with this small, versatile connector for multi-directional data and power delivery.
An increasing number of compact, lithium-ion battery-powered electronics—think wearables, headsets, building automation systems, and medical devices—are getting on the USB-C train. Indeed, the growing usage of lithium-ion (Li-ion) batteries in various consumer devices is contributing to USB-C adoption, as every Li-ion battery-powered device requires power conversions. While the larger, aforementioned electronic devices are leading the charge, smaller portable devices are expected to contribute to USB-C adoption rates of 8.5% per year through 2020, according to ID TechEx. At some point sooner rather than later, USB-C will be the standard for charging and communications, replacing what was once a tangle of different cables to support charging, content streaming, and data transferring.
Designing the charging circuits for USB-C is a unique skillset, compared to the effort involved in designing for legacy USB variants. First and foremost, you need to make sure that the charger and the port controller can talk to each other. Today’s chargers do not have USB-C port control functions built in, so when a USB-C charging source plugs in, the charging won’t start automatically—not ideal for a good user experience. Complex host-side software development is typically required to ensure that analog and digital signals are detected, read, and processed between the charger and controller. You also need to ensure that your design will be able to handle a wide range of power, as this is one of the main advantages of USB-C over its predecessors. Software development is needed here as well as in the host applications processor or microcontroller to properly manage the charger input current limit based on the source capability detected by the port controller IC. (Setting the charger’s input current limit allows the charger to charge the battery at the source’s full capability, which results in faster charging.) In addition, unlike with legacy USB, in Type-C, VBUS is a cold socket at 0V. In order for the source to supply 5V on VBUS, the USB Type-C port controller must establish end-to-end port detection. While USB-C connectors are much smaller than their legacy counterparts, the battery-powered consumer devices that will use them also are shrinking in size (in part because USB-C means fewer required ports on a device). But as the end devices get smaller, the USB-C charging system must follow suit.
USB-C is marked by connectors with a two-fold, rotationally symmetrical design.
Integrated USB-C Buck Charger Simplifies and Shrinks Designs
Creating a smaller charging system design can provide a differentiating advantage, as can producing a more flexible solution that supports backwards compatibility to legacy adapters. Maxim has introduced a USB-C buck charger that eliminates the need for a separate port controller IC, simplifies host software development, and reduces bill of materials (BOM) costs. The MAX77860 is a USB-C 3A switch mode charger that integrates a USB-C port controller and charger IC for 15W applications. As the market’s first integrated USB-C buck charger with integrated CC detection, the IC delivers a simplified and more flexible USB-C charging system design in a 30% smaller solution size versus the closest competitor. The part includes a configuration channel (CC) pin detection feature, so you don’t need to design in this support for end-to-end USB port connection detection (which is required for the USB-C source to deliver power on VBUS). Charging can start automatically without host intervention. The device, available in a 3.9mm x 4.0mm package, also uses a relatively small inductor and capacitor thanks to its high switching frequency (2MHz/4MHz).
The high-efficiency buck in the MAX77860 reduces heat dissipation. The device also supports backwards compatibility with legacy adapters. An integrated 6-channel analog-to-digital converter (ADC) provides accurate voltage and current measurements, while freeing up resources in the microcontroller. The port controller on the device provides plug detection, cable orientation detection, power and data role detection, and VBUS current capability discovery. 5.1V/1.5A reverse boost OTG powers auxiliary devices in USB On-The-Go (OTG) mode.
With their higher speeds, versatility, and small size, USB-C connectors offer a charging, display, and power delivery solution to match the expectations that consumers have for their electronic gadgets. If you’re accustomed to designing for legacy USB standards, however, designing for USB-C does come with some unique challenges. Solutions such as the highly integrated MAX77860 can help simplify the design process while reducing the overall solution size.
For a deeper dive on this topic, read my white paper, “Simplifying Mobile USB-C Designs.”