Simplifying universal serial bus connectivity with USB bridge devices

September 13, 2016

ramyakota-September 13, 2016

The universal serial bus (USB) interface is one of the most successful communication standards in the electronics industry. It has become the standard communication interface for many industrial and consumer applications that require connectivity to a host device. USB’s extreme ease of use coupled with robustness makes it the ideal choice of interface for many embedded applications. However, for embedded designers, a USB implementation requires USB protocol expertise, time-consuming software and firmware development effort.

Most often, designers of these embedded applications are required to provide an end solution that is highly cost effective. The simplest way to achieve this is by integrating the USB functionality in the microcontroller (MCU) along with other peripherals and memory. Many MCU vendors today offer USB-based microcontrollers; however, they may not offer the right peripheral set required for an application, resulting in the need for external components and increased design complexity. There’s also a no-hassle approach for adding USB to any embedded solution, with no need for USB expertise or firmware development, enabling faster times to market for designers.

USB Design Challenges
The ease of use and robustness of USB do not come for free for embedded designers. Developers often have to spend significant time learning the USB protocol and developing a USB stack. This requires specialized tools and can increase development costs and time. There are commercially available USB software stacks; however, they result in additional costs and learning effort.

Another important USB design challenge is the fact that the final product must be compatible with several common operating systems (OS) and keep up with constant OS updates. Developers also must keep the USB hardware costs to a minimum to provide a cost-effective final product. Many USB ICs require external components such as termination resistors or precision oscillators to provide USB functionality. Highly integrated USB solutions with advanced software and tools support are the cornerstone to simplifying USB design.

A Practical Fix: Turnkey USB Connectivity Solutions
Turnkey USB solutions, such as Silicon Labs’ USBXpress bridge devices, provide high integration to eliminate the need for complex firmware and driver development. USB devices with advanced tools support also reduce development time, further simplifying USB connectivity. Highly integrated USB bridge devices can be added to virtually any MCU-based solution to eliminate firmware complexity and reduce development time. These devices act as a bridge to the USB world through the use of standard UART, SPI or I2C interfaces that are readily available on most MCUs.

Bridge devices are especially helpful when developers are upgrading a legacy system with USB communications. Most legacy designs have a specific means of communicating with the host system, in many cases through a UART or I2C interface. A USB-to-UART or USB-to-I2C bridge device, shown in Figure 1, is the best option in this case.

Figure 1. Typical USB-to-UART Bridge (Source: Silicon Labs)

Choosing the Right USB Bridge for Your Application
Embedded designers should consider a multitude of factors when choosing a USB bridge device to ensure seamless USB integration.

First, it is important to minimize hardware design cost that can easily impact an allotted budget. Most USB bridges or MCUs require external components, such as crystal oscillators or termination resistors for USB functionality. Choosing a highly integrated bridge device can eliminate the need for external components including crystal, regulator, and memory, thereby reducing hardware design time and cost.

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