MAX485ESA

The MAX485ESA is a transceiver IC for RS485 and RS422 communication systems, supporting data transmission rates up to 2.5Mbps. The MAX485ESA is a half-duplex RS485 interface chip featuring a Driver Enable (DE) and a Receiver Enable (/RE) control pin. The MAX485ESA receiver is designed with 1/4 unit load input impedance, allowing up to 128 loads on the bus. The MAX485ESA high-speed transceiver for RS485/RS422 communication integrates one driver and one receiver. It features a slew-rate-limited driver that reduces EMI and reflections caused by improper cable termination, enabling data transmission up to 2.5Mbps. In addition to input hysteresis, the MAX485ESA receiver also incorporates an input filter function. This filter improves noise rejection for differential signals with slow rise and fall times. The filter increases receiver propagation delay by 25%. The MAX485ESA has no internal failsafe circuitry. Note that when the differential signal at the A/B pins is between 0.2V and -0.2V (−200mV ≤ A−B ≤ 200mV), the receiver output state is indeterminate. When the receiver input is open (RS485 bus idle), a pull-up resistor must be added to the A pin to ensure the receiver output RO remains high. The MAX485ESA receiver features 1/8 unit load input impedance (128KΩ), allowing up to 128 transceivers to be connected in parallel on the same communication bus. The MAX485ESA slew-rate-limited driver reduces EMI and minimizes reflections caused by improperly terminated cables; the driver rise time is related to the cable length of the termination. Two mechanisms are employed to prevent excessive output current and power dissipation caused by faults or bus contention. First, output stage foldback current limiting provides fast short-circuit protection across the entire common-mode voltage range (refer to typical operating characteristics). Second, a thermal shutdown circuit forces the driver outputs into a high-impedance state when the die temperature exceeds the typical threshold. The transceiver is designed for bidirectional data communication on multipoint bus transmission lines. These devices can also be used as line repeaters for cables longer than 4000 feet. To minimize reflections, the transmission line should be terminated at both ends with its characteristic impedance, and stub lengths beyond the main trunk should be kept as short as possible.

Applications

• Low-power RS485 & RS422 receiver — energy meters, water meters, gas meters
• Level shifting — access control, security systems
• EMI-resistant transceiver — industrial control LAN

Key features

• Tri-state output
• Half-duplex communication ESD protection: Contact discharge: ±5KV, Air discharge: ±5KV (HBM)
• A/B terminal short-circuit protection
• SOP8 package