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RS-485/422 transceivers suit industrial apps

Posted: 10 Dec 2009     Print Version  Bookmark and Share

Keywords:transceiver  RS-485 RS-422 transceiver  communication 

Exar Corp. has unveiled its next-generation 3.3V RS-485/422 transceiver family—the nine device series XR3170E-XR3178E. The transceivers offer a wide range of data rates from 250Kbit/s to 20Mbit/s with high differential output swing (typ. 2.35V), which are suitable for industrial markets including applications such as field bus networks, high-speed motor control, factory automation, building automation, security systems and remote meter reading, among others.

"The higher differential driver output swing enables more reliable communication over longer cable lengths," said Hensen Wong, technical marketing manager of the interface product line. "This benefit provides system architects maximum design flexibility and robust RS-485/RS-422 communications."

The series of RS-485/RS-422 devices is designed for reliable, bidirectional communication on multi-point bus transmission lines. Each device contains one differential driver and one differential receiver. The XR3172E, XR3175E, XR3178E are half-duplex devices, while the XR3170E, XR3171E, XR3173E, XR3174E, XR3176E and XR3177E are full-duplex. All devices comply with TIA/EIA-485 and TIA/EIA-422 standards. Lead-free and RoHS-compliant packages are available for all models.

All devices are ruggedised for use in harsh industrial operating conditions over the entire common-mode voltage range from -7V to +12V. Receivers are specially designed to fail-safe to a logic high output state if the inputs are left undriven or shorted. All RS-485 bus-pins are protected against severe ESD events up to ±15kV (air-gap, EN-61000-4-2 and human body model) and up to ±8kV (contact discharge, EN-61000-4-2). Drivers are protected from excess current flow caused by bus contention or output short-circuits by both an internal current limit and a thermal-overload shutdown. Devices are rated for industrial (-40°C to +85°C) operating temperatures. Receivers have exceptionally high input impedance, which places only one-eighth the standard load on a shared bus. Up to 256 transceivers may co-exist while preserving full signal margin.

All devices operate from a single 3.3V power supply and draw negligible quiescent power. All versions except the XR3171E, XR3174E and XR3177E may independently enable and disable their driver and receiver, and enter a low-power shutdown mode if both driver and receiver are disabled. All outputs maintain high impedance in shutdown or when powered-off.

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