Flexible Internal & External Connectivity for IoT Applications

By Eric Huang, Sr. Product Marketing Manager, USB Controllers

The Internet of Things (IoT) market encompasses a broad range of applications from human-interactive wearables to fully automated machine to machine (M2M) applications used in smart machines, buildings, and entire cities. All of these IoT products have the common requirement of being “always on” or “mostly on” to continuously gather data from the environment and transmit the data to the cloud. While the devices run continuously, they must also minimize power consumption while performing wireless communication and sensor processing tasks.

For the next few years, IoT products will likely ship in volumes below the tens of millions of units annually, which limits the efficiency of designing a single system-on-chip (SoC) to roll out across a broad range market applications. Mobile phones, for example, ship in the tens of millions of units and therefore can use a single, highly integrated SoC with hundreds of functions (and IP cores) on one chip. On the other hand, IoT systems will be assembled and built from multiple discrete ICs as their volumes increase. As a result, connectivity inside an IoT system and on the printed circuit board (PCB) will be extremely important.

The architecture of IoT systems must be designed with the flexibility required to handle different wireless protocols, minimize power consumption, and add new sensor inputs. The natural solution to ensure flexibility is integrating an interface for both internal and external connections. USB is the clear choice. With USB, consumers can plug any device into a PC and it will work. Most tablets, PCs, and mobile phones have at least three internal, on-PCB USB connections for the keyboard, touchpad, touch screen, camera and/or modem, adding up to billions of USB peripheral chips with thousands of functions. USB’s ubiquity in computers, phones, TVs, and set top boxes includes an ecosystem of chips with USB interfaces ready to plug into those devices.

Reduce IoT Power Consumption with USB

Including USB interface on an IoT chip allows the rapid addition of any wireless standard. Volume production of stand-alone wireless chips, like wireless Bluetooth Low Energy chips or WiFi chips, drives down the unit cost, and increases vendor choice for IoT manufacturers. This lowers the overall cost of the bill of materials.

USB also enables lower power consumption. USB reduces overall power consumption by turning on the controller (and PHY) quickly, transmitting, and then turning off quickly. The USB and the wireless chip are only fully active, when data is transmitting. USB enables the architecture needed to reduce system bill of material costs, allows the leveraging of existing USB software drivers, and increases overall flexibility of the design.

IoT System Architecture

For maximum flexibility at the system level to hit a broad range of markets, an IoT chip will typically be limited in functionality to a microprocessing unit (MPU) and interfaces. The interfaces will go to standard peripherals and sensors in the system. These connect within the system on the PCB. IoT chips usually have a minimum of three USB host ports and one USB device port. The ports can be used either internal to the system/box, or for external connections to peripherals. 

USB inside the box

For IoT, more ports will be used inside the box for internal connections to wireless chips, sensors, or input devices. By using USB on the PCB, the product maker can choose from a wide range of commercially available wireless or other chips to expand functionality. As customers request customization, product makers can select the specific wireless standards, sensors or other peripherals as requested. 

USB outside the box

Externally, IoT devices will likely have only one USB Type-C port. The port can be used for continuous charging, firmware updates, data downloads, diagnostics, or to connect to another device.

Most wireless chips have a USB 1.1, USB 2.0, or USB 3.0 interface (Figure 1). Modems often have a High-Speed Interchip (HSIC) interface, which reduces the number of FR4 traces on the PCB from the IoT MPU to the modem. HSIC uses one-third the power of a USB 2.0 PHY because is exclusively for use on a PCB, and not for transmitting data over a USB cable. HSIC is only found on modems.

Figure 1: SoC for IoT using USB 2.0 Host & Device for wireless communication

By including USB connections both inside the box and outside the box (Figure 2), IoT chips will be better able to address the primary IoT markets. 

Figure 2: IoT system using USB 2.0 for external wired/wireless communication 

USB in IoT Market Segments

For this discussion, IoT Market Segments will be grouped into 3 categories: wearables for consumers, M2M for short distances within buildings, and M2M for smart cities.

For wearables, battery life and quick charging is paramount. Consumers charge these devices using a cradle or a USB port directly on the device. The cradle may have simple electrical contacts or wireless charging. The wearable device itself will use Bluetooth LE (BLE) to synchronize data gathered (or delivered to it) to a mobile phone, tablet or PC. Some wearables will use a touchscreen or a camera.

M2M products within buildings will have WiFi or Zigbee, and possibly BLE for connection to a server in the cloud. Some M2M products will be battery operated or solar powered. For the M2Ms tethered to a power outlet, a small, single USB Type-C connector is ideal. The same, single port could be used for programming or debugging when over-the-air isn’t possible. The same port can be used for both setup and power, and can reduce the overall cost of the product by eliminating one connector.

M2M products for smart cities will connect by a modem or WiFi to a network. It may call in periodically to upload data, once a day, or multiple times an hour, or continuously. It may be solar powered or tethered to a power source. The sensors may measure weather, traffic, air quality, or data needed for municipal operations. They may also provide remote control from a central control center to the IoT location. These require great flexibility and durability and must be easy to maintain. A standard USB connector is easy to use and easy to replace. When an IoT module needs to be replaced, simply unplug the device and plug in a new one with no custom wiring required.

USB Type-C Advantages for IoT

In addition to the small form factor connector and cable, the USB Type-C standard offers a flippable, durable connector, and more power delivery than the earlier USB connectors. The new USB Type-C standard supports two different voltage/amperage levels. The higher level provides more power than the Battery Charging standard alone. Battery Charging can provide 7.5 W but requires additional circuitry, usually as a separate chip in a product. By using a standard Type-C PHY and controller, the Battery Charging chips and cost can be eliminated. A Type C implementation can provide 15 W of charging power without the additional circuitry and associated board space. Type C can be implemented cheaply and easily in USB 2.0 and USB 1.1 designs, and fully integrated into USB 3.0 designs with the right IP implementation. 

USB for IoT

Product makers can quickly assemble or customize IoT products in full systems by leveraging the ubiquity of USB to add features their customers demand. By reusing chips and software drivers, IoT product makers can deliver products to market quickly. In addition, the USB Type-C connector provides additional power delivery in a small form factor connector and cable with easier maintenance. USB is ideal for both internal and external connections in IoT products.