High-throughput USB to serial bridge ICs

September 22, 2014 // By Graham Prophet
Aimed at industrial applications, a family of USB to serial bridge devices provides a straightforward way to interface with RS-232 or RS-485 serial networks through USB using a minimum of components and PCB space.

The XR21B1420, XRB21B1422, and XRB21B1424 provide 1, 2, and 4 UART channels respectively. The XRB21B1421 provides a single channel UART and uses the native operating system HID (Human Interface Device) driver.

The XR21B142x devices are fully compliant to the USB 2.0 (Full-Speed) specification with 12 Mbps USB data transfer rate, and deliver significantly higher data throughput compared to competing devices, especially when multiple channels are operating simultaneously. 512-Byte transmit (TX) and receive (RX) FIFOs enable a maximum data throughput of 9 Mbps across up to four UART channels.

“While nearly all new processors and MCUs include numerous USB ports, legacy peripherals and networks remain RS-232 or RS-485/422. This drives a continued need to bridge USB to serial protocols” said John Cantelmo, vice president of Connectivity Products at Exar.

The parts have ±15kV Electro-Static Discharge (ESD) protection on the USB pins, eliminating the need for additional protection components. This makes these devices ideal for rugged applications such as smart grid data collection, data aggregators and concentrators, security and access control systems, ATM and gaming terminals, and rugged USB to serial converters. The devices feature an internal oscillator, removing the need for an external crystal. They can be powered directly from the USB host's 5V supply and an integrated LDO provides a regulated 3.3V power supply output, removing the need for an external LDO.

The XR21B1421 uses the native HID drivers in Windows, Linux, and Mac OS X distributions, removing the need for installing custom drivers, simplifying the integration process; however, it requires an assigned port. The XR21B1420/2/4 devices use native OS CDC-ACM drivers, or a custom driver to activate advanced features. Exar provides WHQL/HCK-certified software drivers for Windows 2000, XP, Vista, 7, 8, 8.1 as well as drivers for Windows CE, Linux and Mac OS X. Full source code is provided on request.

The XR21B142x family supports USB suspend, resume and remote wakeup operations. Any baud rate up to 12 Mbps