Description

The MAX3080E–MAX3089E are ±15kV electrostatic discharge (ESD)-protected, high-speed transceivers for RS485/RS-422 communication that 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 MAX3086E/MAX3087E/ MAX3088Es’ driver slew rates are not limited, making transmit speeds up to 10Mbps possible. The MAX3089E’s slew rate is selectable between 115kbps, 500kbps, and 10Mbps by driving a selector pin with a single three-state driver. All devices feature enhanced ESD protection. All transmitter outputs and receiver inputs are protected to ±15kV using the Human Body Model.

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 MAX3080E/MAX3081E/ MAX3083E/MAX3084E/MAX3086E/MAX3087E are intended for full-duplex communications.

 

Features

ESD Protection for RS-485 I/O Pins ±15kV, Human Body Model

True Fail-Safe Receiver While Maintaining EIA/TIA-485 Compatibility

Allow Up to 256 Transceivers on the Bus

 

Applications

RS-422/RS-485 Communications

Level Translators

Transceivers for EMI-Sensitive Applications

Industrial-Control Local Area Networks

 

Applications Information

The MAX3080E–MAX3089E 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 the Fail-Safe section).

The MAX3086E/MAX3087E/MAX3088E’s driver slew rates are not limited, making transmit speeds up to 10Mbps possible.

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.

The MAX3080E family guarantees a logic-high receiver output when the receiver inputs are shorted or open, or when they are connected to a terminated transmission line with all drivers disabled. This is done by setting the receiver threshold between -50mV and -200mV. If the differential receiver input voltage (A – B) is greater than or equal to -50mV, RO is logic high. If A – B is less than or equal to -200mV, RO is logic low. In the case of a terminated bus with all transmitters disabled, the receiver’s differential input voltage is pulled to 0V by the termination. With the receiver thresholds of the MAX3080E family, this results in a logic high with a 50mV minimum noise margin. Unlike previous fail-safe devices, the -50mV to -200mV threshold complies with the ±200mV EIA/TIA-485 standard.

ESD-protection structures are incorporated on all pins to protect against electrostatic discharges encountered during handling and assembly. The driver outputs and receiver inputs of the MAX3080E–MAX3089E family have extra protection against static electricity. Maxim’s engineers have developed state-of-the-art structures to protect these pins against ESD of ±15kV without damage.

The Machine Model for ESD tests all pins using a 200pF storage capacitor and zero discharge resistance. The objective is to emulate the stress caused when I/O pins are contacted by handling equipment during test and assembly. All pins require this protection, not just RS-485 inputs and outputs.

The standard RS-485 receiver input impedance is 12kΩ (one-unit load), and the standard driver can drive up to 32 unit loads. The MAX3080E family of transceivers have a 1/8-unit-load receiver input impedance (96kΩ), allowing up to 256 transceivers to be connected in parallel on one communication line. Any combination of these devices and/or other RS-485 transceivers with a total of 32 unit loads or less can be connected to the line.