STMICROELECTRONICS’ RS-485 TRANSCEIVERS COMBINE ROBUST SIGNALING WITH SUPERIOR SPEED

The ST4E1240 is the first in a new family of transceivers from ST featured to deliver robust and reliable RS-485 signaling for modern, performance-hungry industrial applications. The new transceivers support data speeds far above the original RS-485 standards and allow multipoint connections over extended cable runs with more than 64 transceivers on the bus. Typical uses are in programmable logic controllers (PLCs), robots, telecom infrastructures, smart-building controls, servo drives, optical networking devices, grid infrastructure, data-acquisition systems including smart meters, and backplane buses.

The protection built into the ST4E1240 meets IEC 61000-4-2 up to +/-12kV contact discharge, allowing the devices to be used without external ESD protection. There is also class-A fast-transient protection up to +/- 4kV, meeting IEC 61000-4-4, ensuring data integrity and bus stability. Hot-swap circuitry prevents unwanted states on the bus during device switch-on or plug-in and is capable of discharging up to 100pF parasitic capacitance. Furthermore, the transceiver integrates failsafe protection that drives the output high to avoid an indeterminate state upon detecting an open, shorted, or idle bus. Other features include 250mA short-circuit protection and thermal shutdown.

The ST4E1240 fulfils all TIA/EIA-485 (RS-485) standards and ensures the output differential voltage exceeds 2.1V, at 5V supply, for compatibility with the popular PROFIBUS field bus standard. There is also a shutdown mode, controlled with external enable pins, that reduces the quiescent current below 3.5µA for use in energy-conscious applications.