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-Safe section). 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

Reflections section). 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 trans-

ceivers. 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 shut-

down circuitry places the driver outputs into a high-

impedance state.

Receiver Input Filtering

The receivers of the MAX3080–MAX3085, and the

MAX3089 when operating in 115kbps or 500kbps

mode, incorporate input filtering in addition to input

hysteresis. This filtering enhances noise immunity with

differential signals that have very slow rise and fall

times. Receiver propagation delay increases by 20%

due to this filtering.

Fail-Safe, High-Speed (10Mbps),

Slew-Rate-Limited RS-485/RS-422 Transceivers

14

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DIP/SO

TOP VIEW

1

2

3

4

5

6

7

14

13

12

11

10

9

8

RXP

TXP

A

B

Z

Y

RO

RE

DE

DI

SRL

GND

H/F

MAX3089

RD

TXP

A

B

Z

Y

GND

DE

SRL

DI

MAX3089

H/F

RE

NOTE: SWITCH POSITIONS

INDICATED FOR H/F = GND

Figure 4. MAX3089 Pin Configuration and Functional Diagram