10/15/02

SP3481/3485 Low Power Half-Duplex RS485 Transceivers

© Copyright 2000 Sipex Corporation

4

PIN FUNCTION

Pin 1 – RO – Receiver Output.

Pin 2 – RE – Receiver Output Enable Active LOW.

Pin 3 – DE – Driver Output Enable Active HIGH.

Pin 4 – DI – Driver Input.

Pin 5 – GND – Ground Connection.

Pin 6 – A – Driver Output/Receiver Input

Non-inverting.

Pin 7 – B – Driver Output/Receiver Input Inverting.

Pin 8 – V

CC

DESCRIPTION

The SP3481 and the SP3485 are 2 members

in the family of +3.3V low power half-duplex

transceivers that meet the specifications of the

RS-485 and RS-422 serial protocols. These

devices are pin-to-pin compatible with the Sipex

SP481, SP483, and SP485 devices as well as

popular industry standards. The SP3481 and

the SP3485 feature Sipex's BiCMOS process

allowing low power operation without sacrificing

performance.

Drivers

The driver outputs of the SP3481 and SP3485

are differential outputs meeting the RS-485 and

RS-422 standards. The typical voltage output

swing with no load will be 0 Volts to +3.3 Volts.

With a load of 54

Ω across the differential

outputs, the drivers maintain greater than

1.5V voltage levels. The drivers of the SP3481

and SP3485 have an enable control line which

is active HIGH. A logic HIGH on DE (pin 3)

will enable the differential driver outputs.

A logic LOW on DE (pin 3) will tri-state the

driver outputs.

The tranceivers in the SP3481 and SP3485

operate up to 10Mbps. The 250mA I

SC

maximum limit on the driver output allows

the SP3481 and the SP3485 to withstand an

infinite short circuit over the -7.0V to +12.0V

common mode range without catastrophic

damage to the IC.

SP3481/SP3485

Pinout (Top View)

RO 1

RE 2

DE 3

DI 4

8

7

B

6

A

5

GND

D

R

SP485

Top View

Receivers

The SP3481 and SP3485 receivers have

differential inputs with an input sensitivity as

low as

±200mV. Input impedance of the

receivers is typically 15k

Ω (12kΩ minimum).

A wide common mode range of -7V to +12V

allows for large ground potential differences

between systems. The receivers of the SP3481

and SP3485 have a tri-state enable control pin.

A logic LOW on RE (pin 2) will enable the

receiver, a logic HIGH on RE (pin 2) will disable

the receiver.

The receivers of the SP3481 and SP3485 operate

up to 10Mbps. The receiver for each of the three

devices is equipped with fail-safe. Fail-safe

guarantees that the receiver output will be in a

HIGH state when the input is left unconnected.

Shutdown Mode for the SP3481

The SP3481 is equipped with a Shutdown mode.

To enable the Shutdown state, both the driver

and receiver must be disabled simultaneously.

A logic LOW on DE (pin 3) and a logic HIGH on

RE (pin 2) will put the SP3481 into Shutdown

mode. In Shutdown, supply current will drop to

typical 1

µA, 10µA maximum.