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10/16/02

SP3493/3494 +3.3V Low Power Slew-Rate Limited RS-485/RS-422 Transceivers

© Copyright 2002 Sipex Corporation

DESCRIPTION

The SP3493/3494 are +3.3V transceivers that

meet the electrical specifications of the

RS-485 and RS-422 serial protocols. The

SP3493/3494 feature Sipex's BiCMOS process

allowing low power operation without

sacrificing performance.

The SP3493 device is a +3.3V full-duplex

transceiver that is pin-to-pin compatible with

the Sipex SP3490 and SP490 devices as well as

popular industry standards such as the

MAX3488, the LTC490, and the 75179. The

SP3493 has a driver with a data transmission

rate of 250kbps.

The SP3494 device is a +3.3V half-duplex

transceiver that is pin-to-pin compatible with

the Sipex SP3481 and SP481 devices as well as

popular industry standards such as the MAX3486

and the 75176. The SP3494 has a partially slew-

rate limited driver with a data transmission rate

of 2.5Mbps.

Drivers

The SP3493/3494devices both have differential

outputs. The typical voltage output swing with

no load will bo 0V to V

loading of 54

Ω across the differential outputs,

the driver can maintain greater than 1.5V voltage

levels.

The SP3494 device has 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 force the driver

outputs at high impedance (high-Z). The SP3493

device does not have a driver enable.

The SP3493/SP3494 drivers will operate up to

250kbps and 2.5Mbps, respectively. In addition

to adhering to the 250mA I

the driver output, the driver output short-circuit

protection will allow the devices to withstand an

infinite short circuit over the -7.0V to +12V

common mode range without damage.

Receivers

The receivers have differential inputs with an

input sensitivity as low +200mV. Input

impedance of the receivers is typically 15k

Ω

(12k

Ω minimum). A wide common mode range

of -7V to +12V allows for large ground potential

differences between systems.

Both the SP3493/SP3494 receivers are

equipped with fail-safe which guarantees that

the receiver outputs will be in a high state

when the input is left unconnected.

The SP3494 receiver has a high impedance

(high-Z) 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 SP3494 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 SP3494 into shutdown.

In shutdown, the supply current will drop to 2nA

typical, 1

µA maximum.