Multiprotocol transceiver is a total solution for traditional serial standards

February 11, 2014 // By Graham Prophet
With internally switched termination, and occupying a 5 x 5 mm package, Exar’s SP335 multiprotocol transceiver supports RS-232, RS-485, and RS-422 serial standards.

At 5 x 5 mm, the SP335 is less than half the size of a comparable discrete design, doubling the number of serial interface channels that can be assembled in the same board space and allowing you to combine multiple serial protocols over the same connector. Programmable end-of-line termination and multiple configuration modes allow all three protocols to be used interchangeably over a single cable or connector with no additional switching components.

The SP335’s bus pins are protected against ESD events exceeding ±15 kV IEC 61000-4-2 Air Gap Discharge, and ±8 kV IEC 61000-4-2 Contact Discharge, and can tolerate direct shorts to DC or AC voltages as high as ±18V. These rugged devices are intended for use in software programmable serial ports for industrial PCs and single board computers, process control, point-of-sale, embedded systems, HVAC controls, building automation networking, and security systems. The SP335 also has a separate supply voltage for the logic interface pins, allowing the part to directly interface with low voltage UARTs and MCUs without needing voltage translators or level shifters. The logic supply voltage can be as low as 1.65V.

The SP335 is the smallest of a series of dual protocol devices:

• SP335 – 2-driver/2-receiver RS-232 – 1-driver/1-receiver RS-485/422

• SP336 – 4-driver/4-receiver RS-232 – 2-driver/2-receiver RS-485/422

• SP337 – 3-driver/5-receiver RS-232 – 2-driver/2-receiver RS-485/422

• SP338 – 3-driver/5-receiver RS-232 – 2-driver/4-receiver RS-485/422

• SP339 – 3-driver/5-receiver RS-232 – 1-driver/1-receiver RS-485/422

The SP335 supports data rates up to 20 Mbps in RS-485/422 modes (1 Mbps in RS-232) and can be slew limited to 250 kbps in any mode by toggling a single control pin. The on-board charge pump generates the RS-232 bipolar voltage levels from a single supply (3.0V to 5.5V) with only four external capacitors, and does not require any inductors or magnetic components. It costs $4.35 (1000).