Fault-tolerant transceivers with Level 4 IEC ESD protection

November 13, 2013 // By Graham Prophet
Exar's XR3070-78X family of ruggedised RS-485/RS-422 transceivers for harsh industrial environments operate from 3.3V with ±18V fault tolerance.

Their analogue bus pins can withstand direct shorts up to ±18V and are protected from ESD events exceeding IEC Level 4. Operating from 3.3V with 300 μA idle current, these devices consume half the power of a comparable ±18V fault-tolerant solution. The family of nine devices supports data rates up to 20 Mbps in either full or half duplex configurations, and is intended for use in energy metering, building automation, security systems, process control, and other industrial automation applications.

“ESD and over-voltage events are leading causes of field failures and equipment returns in industrial communication applications,” said Jack Roan, product marketing manager, Exar. “The XR3070-78X family delivers robust protection in both these areas.”

Common practice in these applications is to route 15 Vdc or 12 Vac power in the same cable pack as the RS-485 data lines. Damaged cables or incorrect wiring can expose the transceiver to these voltages, which will permanently damage standard RS-485 devices. The XR3070-78X provides cost effective insurance against wiring faults up to ±18V, and simultaneously protects against ESD events exceeding IEC Level 4. The IEC standard is significantly more stringent than the Human Body Model (HBM) ESD test commonly referenced by semiconductor device manufacturers, mainly due to the higher currents requirements.

XR3070-78X are 1-driver/1-receiver RS-485/422 devices operating from a 3.0V to 3.6V power supply (3.3V ±10%) and are fully compliant to the TIA/EIA-485 and TIA/EIA-422 standards. The bus pins feature enhanced ESD protection to ±15 kV (±15 kV IEC 61000-4-2 Air Gap Discharge, ±8 kV IEC 61000-4-2 Contact Discharge, ±15 kV Human Body Model); non-bus pins are protected up to ±4 kV Human Body Model.

The XR3070-78X family is available in standard 8 NSOIC and 14 NSOIC packages at $1.25 (1000).

Exar; www.exar.com