6

SP431DS/08

SP431 High Speed, +3.3V Quad RS-422 Differential Line Driver

© Copyright 1997 Sipex Corporation

DESCRIPTION

The SP431 is a low-power quad differential line

driver designed for digital data transmission

meeting the specifications of the EIA standard

RS-422 serial protocol. The SP431 features

Sipex's BiCMOS process allowing low power

operational characteristics of CMOS technol-

ogy while meeting all of the demands of the

RS-422 serial protocol up to 60Mbps under load

in harsh environments.

The RS-422 standard is ideal for multi-drop

applications and for long-distance communica-

tion.

The RS-422 protocol allows up to 10

drivers to be connected to a data bus, making it

an ideal choice for multi-drop applications. Since

the cabling can be as long as 4,000 feet, RS-422

drivers are equipped with a wide common mode

output range to accommodate ground potential

differences. Because the RS-422 is a differential

interface, data is virtually immune to noise in

the transmission line.

The SP431 accepts TTL or CMOS input levels

and translates these to RS-422 output levels. The

SP431 features active HIGH and active LOW

driver enable controls common to all four driver

channels see Figure 8. A logic HIGH on the

ENABLE pin (pin 4) or a logic LOW on the

ENABLE pin (pin 12) will enable the differential

driver outputs. A logic LOW on the ENABLE

pin (pin 4) or a logic HIGH on the ENABLE pin

(pin 12) will tri-state the driver outputs.

Figure 7. Two-Wire Balanced System, RS-422

ENABLE

ENABLE

DATA

DATA

OUTPUT

recommended to reduce reflection.

The RS-422 line driver outputs feature high

source and sink current capability. All drivers

are internally protected against short circuits on

their outputs. The driver outputs are short-circuit

limited to 150mA. The driver output skew times

are typically 0.5ns.

To minimize reflections, the multipoint bus

transmission 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.

Figure 8. Truth Table, Enable / Disable Function

Common to All Four RS-422 Drivers

E

L

B

A

N

EE

L

B

A

N

Et

u

p

n

I

-

n

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N

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t

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p

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u

Ot

u

p

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t

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p

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u

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O

W

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LH

G

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He

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-

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te

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H

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c

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dW

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LW

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HH

G

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HW

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