Inventing the future

News Release from: Intersil
Subject: ISL8487, ISL81483 and ISL81487
Edited by the Electronicstalk Editorial Team on 28 November 2003

Fractional-load transceivers extend serial comms

Three new Linearlink RS485/422 fractional-load serial data transceivers operate from a nominal 5V supply over a wide +/-10% tolerance range that relaxes supply requirements and reduces costs.

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Intersil has released three new Linearlink RS485/422 serial data transceivers, the ISL8487, ISL81483 and ISL81487. All three ICs are half-duplex fractional-load transceivers that operate from a nominal 5V supply over a wide +/-10% tolerance voltage range of +4.5 to +5.5V, which relaxes supply requirements and reduces costs. The quiescent current for these devices is extremely low and the ISL8487 and ISL81483 become almost invisible in the shutdown mode with a miniscule 1nA drip.

In addition, these new devices are designed to cause less bus loading with lower input current than competing ICs that they replace.

Applications for these fractional-load transceivers include, but are not limited to, factory automation, security networks, process control, plant environmental control and remote sensing and metering.

An example of a wide-spanning high-density network is utility meter data collection in a large apartment complex or condominium.

Fractional-load transceivers increase the number of devices allowed on the bus up to 256 from the traditional single unit load limit of 32 eliminating the need for repeaters.

The ISL8487 is a quarter-unit load device that enables up to 128 nodes because each ISL8487 transceiver is one-quarter the load of a standard unit-load device.

Four ISL8487 transceivers have the bus loading effect of one single-unit-load transceiver.

The ISL81483 and ISL81487 are eighth-unit load devices that enable up to 256 nodes.

Thus, these fractional-unit load devices allow larger node counts while remaining under the RS485 mandated 32 unit load limit.

These transceivers meet both RS485 and RS422 standards for balanced (differential) communication.

The ISL8487 and ISL81483 are slew-rate limited for error free data transmission in applications where the data rate is less than 250Kbit/s, typically used for long data-collecting networks, up to 1.2km.

Slew-rate limiting reduces EMI and minimises reflections from improperly terminated transmission lines, or unterminated stubs in multidrop and multipoint applications.

The ISL81487 can operate up to 5Mbit/s for high-speed applications over shorter networks.

The ISL8487, ISL81483 and ISL81487 are half-duplex transceivers whose receive (Rx) and transmit (Tx) functions are multiplexed, reducing package size and pin count to only eight leads.

Rx inputs feature a fail-safe-if-open design, which ensures a logic high Rx output if Rx inputs are floating.

This prevents the Rx output from chattering, and accidentally generating interrupts, if the receiver becomes disconnected from the bus.

A "lockout" feature on the ISL8487 and ISL81483 keeps the Rx output disabled, when exiting shutdown, until the Rx has determined what state it should go to.

This prevents the Rx output from accidentally generating an interrupt while the Rx wakes up.

Driver outputs are short circuit protected, even for voltages that exceed the supply voltage.

Additionally, on-chip thermal shutdown circuitry disables the Tx outputs to prevent damage if power dissipation becomes excessive.

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