Which flavor of USB should be chosen when designing an IoT SoC?
USB is ubiquitous for a reason – It was designed specifically to be easy for consumers to use. When designers working in the fast-growing Internet of Things (IoT) market are looking for interfaces that can help with everything from charging to data transfer, USB is top-of-mind. However, IoT applications have performance, power and area requirements that are quite different from your phone or desktop computer. In addition, a single system-on-chip (SoC) design may be used in multiple end applications, making system flexibility a critical consideration. With this new set of requirements, designers are turning back to the tried-and-true USB 2.0, but using new versions that provide the flexibility, power, and area needed for IoT applications – as well as USB Type-C support.
IoT SoCs – one chip, many applications
Due to the cost of silicon, SoC platforms need to be manufactured in the millions and be flexible enough to be easily customized for multiple IoT products and applications. The chip lots can be broken into hundreds of individual IoT applications, each of which will sell tens of thousands. So the standard IoT chip platform will have a few key features produced in volume, with many other features customized to the specific application.
IoT products fall into three broad categories: wearables, smart buildings, and smart cities. Each product category has different features, but they also have common requirements to provide those features. When designing a platform for IoT, the platform must be flexible enough to accommodate the different requirements. The hardware specifically must be able to connect to connectivity, sensor, control, and power components. The exact requirements will vary based on the design of the product. For example, some IoT devices will have no controls since all the control will be via a smartphone or tablet or a central control center.
IoT SoC Connectivity
USB is attractive for connectivity and controls because it’s easy to prototype an application by buying off-the-shelf chips and plugging them in via USB. In just a few hours, designers can have, for example, an IoT platform running Wi-Fi data connected to a USB camera or sensors. The sensors themselves can vary from high-speed inspection cameras in a manufacturing environment, which require USB 3.0 (5 Gbps) or 3.1 (10 Gbps) speeds, to most IoT sensors, where USB 2.0 (480 Mbps) will suffice.
Ease of USB driver development
The use of USB allows features to be added by a chip on a PCB and inside the system. It also allows for rapid customization externally. USB host drivers are widely available in Linux and other open source operating systems, saving designers from needing to build their own. Whether the features are added by a chip on the PCB, or through external connection, they both use exactly the same driver, which is an advantage over interfaces like I2C or PCIe which require different drivers. In this case, a single software driver can be used for the internal or external addition of a feature or function.
Why USB 2.0 instead of USB 3.0 or 3.1, I2C, or other interface options?
USB 3.1 is the latest USB-IF standard, running at 10 Gbps. USB 3.0 at 5 Gbps is by far the most popular generation for most new consumer products. However, for IoT, USB 2.0 running at only 480 Mbps is usually the right choice. USB 2.0 offers much lower power consumption and smaller area use than USB 3.0 – as small as 10% the size of a USB 3.0 solution, at about half the active power use. Even at effective speeds of only 320 Mbps, USB 2.0 offers fast enough transfer speeds for debugging and firmware updating, and the low power consumption and small area make it the ideal interface for IoT.
Type-C advantages – ease of use, durability
For IoT edge devices, ease of use and durability are key to every design. The new Type-C connector adds additional ease-of-use and durability to USB, making it even more attractive for use for external connections. The connector is symmetrical. This allows insertion/connection in both the up and down orientation. This reduces the stress the user places on the connector when plugging in a cable. In addition, the connector was designed for more insertions and removal. The small form factor allows it to be used in smaller devices, like charging cradles for wearables.
The Type-C standard also allows for a range of power options. It provides up to 15W of power, double that of previous USB connector standards. This enables either faster charging or more features to be actively used in the IoT system.
USB 2.0 IP for IoT
Consumers and other end-users use USB for charging and data transfer. System makers use USB for debug and firmware updates externally, and for adding functionality internally and externally. With the new, small-form factor Type-C connector which is even easier to use than the older USB connectors, USB becomes even more attractive for designers to integrate as the primary interface both internally and externally in IoT systems. Synopsys’ USB 2.0 for IoT is a great fit for IoT applications. Its small area keeps the cost of IoT chips as low as possible. The IP architecture, based on hundreds of years of engineering expertise, has shipped in billions of units, making it both reliable and low risk to implement.