General Description

The MAX3080–MAX3089 high-speed transceivers for RS-485/RS-422 communication contain one driver and one receiver. These devices feature fail-safe circuitry, which guarantees a logic-high receiver output when the receiver inputs are open or shorted. This means that the receiver output will be a logic high if all transmitters on a terminated bus are disabled (high impedance).

The MAX3080/MAX3081/MAX3082 feature reduced slew-rate drivers that minimize EMI and reduce reflections caused by improperly terminated cables, allowing error-free data transmission up to 115kbps.

These transceivers typically draw 375µA of supply current when unloaded, or when fully loaded with the drivers disabled.

All devices have a 1/8-unit-load receiver input impedance that allows up to 256 transceivers on the bus. The MAX3082/MAX3085/MAX3088 are intended for halfduplex communications, while the MAX3080/MAX3081/ MAX3083/MAX3084/MAX3086/MAX3087 are intended for full-duplex communications. The MAX3089 is selectable between half-duplex and full-duplex operation. It also features independently programmable receiver and transmitter output phase via separate pins.

 

Applications

RS-422/RS-485 Communications

Level Translators

Transceivers for EMI-Sensitive Applications

Industrial-Control Local Area Networks

 

Next Generation Device Features

For Fault-Tolerant Applications: MAX3430: ±80V Fault-Protected, Fail-Safe, 1/4 Unit Load, +3.3V RS-485 Transceiver

For Low-Voltage Applications: MAX3362: +3.3V, High-Speed, RS-485/RS-422 Transceiver in a SOT23 Package

For Multiple Transceiver Applications: MAX3030E–MAX3033E: ±15kV ESD-Protected, +3.3V, Quad, RS-422 Transmitters MAX3040–MAX3045: ±10kV ESD-Protected, Quad, +5V, RS-485/RS-422 Transmitters

 

Detailed Description

The MAX3080–MAX3089 high-speed transceivers for RS-485/RS-422 communication contain one driver and one receiver. These devices feature fail-safe circuitry, which guarantees a logic-high receiver output when the receiver inputs are open or shorted, or when they are connected to a terminated transmission line with all drivers disabled (see Fail-Safesection). The MAX3080/ MAX3081/MAX3082 feature reduced slew-rate drivers that minimize EMI and reduce reflections caused by improperly terminated cables, allowing error-free data transmission up to 115kbps (see Reduced EMI and Reflectionssection). The MAX3083/MAX3084/MAX3085 offer higher driver output slew-rate limits, allowing transmit speeds up to 500kbps. The MAX3086/ MAX3087/MAX3088’s driver slew rates are not limited, making transmit speeds up to 10Mbps possible. The MAX3089’s slew rate is selectable between 115kbps, 500kbps, and 10Mbps by driving a selector pin with a three-state driver.

The MAX3082/MAX3085/MAX3088 are half-duplex transceivers, while the MAX3080/MAX3081/MAX3083/ MAX3084/MAX3086/MAX3087 are full-duplex transceivers. The MAX3089 is selectable between half- and full-duplex communication by driving a selector pin high or low, respectively.

All of these parts operate from a single +5V supply. Drivers are output short-circuit current limited. Thermal shutdown circuitry protects drivers against excessive power dissipation. When activated, the thermal shutdown circuitry places the driver outputs into a highimpedance state.

 

Applications Information

Typical Applications

The MAX3082/MAX3085/MAX3088/MAX3089 transceivers are designed for bidirectional data communications on multipoint bus transmission lines. Figures 21 and 22 show typical network applications circuits. These parts can also be used as line repeaters, with cable lengths longer than 4000 feet, as shown in Figure 17.

To minimize reflections, the line should be terminated at both ends in its characteristic impedance, and stub lengths off the main line should be kept as short as possible. The slew-rate-limited MAX3082/MAX3085, and the two modes of the MAX3089, are more tolerant of imperfect termination.

 

Driver Output Protection

Two mechanisms prevent excessive output current and power dissipation caused by faults or by bus contention. The first, a foldback current limit on the output stage, provides immediate protection against short circuits over the whole common-mode voltage range (see Typical Operating Characteristics). The second, a thermal shutdown circuit, forces the driver outputs into a high-impedance state if the die temperature becomes excessive.