Electronic Design

RS-485/RS-422 Serial Transceivers Now Can Hit 32 Mbits/s

The popular RS-485 and RS-422 serial data networks used in industrial automation can now be made better than ever thanks to Exar’s SP349x series of transceivers, which offer data rates to 32 Mbits/s and increased line protection. They’re also pin-compatible with Exar’s previous SP349x series transceivers. When designing new RS-485 and RS-422 hardware and next-generation industrial networks for process control, plant environmental control, and remote sensing and metering applications, you can get the extra speed often demanded.

The SP3495E is a half-duplex RS-485 transceiver, while the SP3496E and RS3497E are full-duplex RS-485 transceivers. They all permit the implementation of bidirectional communications on a single multipoint/multidrop balanced bus transmission line. Each device contains one differential driver and one differential receiver. The family offers several choices: half-duplex, full-duplex, or full-duplex with enable/shutdown. Separate enable pins control the driver and receiver independently or may be externally connected together as a direction control.

The transceivers operate from a single 3.3-V power supply and load the data bus only half as much as a standard RS-485 unit-load. This allows up to 64 devices to be connected simultaneously on a bus without violating required RS-485 signal margin and without using repeaters. Short-circuit protection and thermal shutdown prevent excessive power dissipation caused by bus contention or by shorting outputs to ground or a voltage source. This forces the driver output into a high impedance state if the absolute value of the output current exceeds 250 mA or if junction temperature exceeds 165°C.

The advanced fail-safe feature guarantees a logic-high receiver output if the receiver’s differential inputs are shorted, open-circuit, or shunted by a termination resistor. All inputs and outputs have electrostatic discharge (ESD) protection. Bus-pins are ESD protected up to ±15 kV Human Body Model. Robust ESD protection, advanced fail-safe specifications, and hot-swap glitch protection are all vital features for critical applications like precision control of motor positioning in factory automation systems with high-speed communication.

Samples of the SP3495E and SP3496E are available now in an eight-pin small-outline (SOIC) package supporting the –40°C to 85°C temperature range. In addition, samples of the SP3497E are available in a 14-pin SOIC package supporting the –40°C to 85°C temperature range. Lead-free and packages that comply with the European Union’s Restrictions on Hazardous Substances (RoHS) are available. In 1000-piece quantities, the SP349xE family price is $1.25.

Exar Corp.


TAGS: Components
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