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Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7000 • www.exar.com

SP3485_200_051916

The

SP3485 is a member in the family of

+3.3V low power half-duplex transceivers

that meet the electrical specifications of the

RS-485 and RS-422 serial protocols. This

device is pin-to-pin compatible with the

Exar

SP481, SP483 and SP485 devices as well

as popular industry standards. The

SP3485

feature

Exar's BiCMOS process allowing

low power operation without sacrificing

performance.

Driver

The driver outputs of the

SP3485 are dif-

ferential 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 54Ω across the

differential outputs, the drivers can maintain

greater than 1.5V voltage levels.

The driver of the

SP3485 has a driver enable

control line which is active HIGH. A logic

HIGHonDE(pin3)willenablethedifferential

driver outputs. A logic LOW on the DE (pin

3) will tri-state the driver outputs.

The driver of the SP3485 operates up to

10Mbps. The 250mA I

on the driver output allows the SP3485 to

withstand an infinite short circuit over the

-7.0V to +12V common mode range without

catastrophic damage to the IC.

Receiver

The

SP3485 receiver has differential inputs

with an input sensitivity of ±200mV. Input

impedance of the receiver is 12kΩ minimum.

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

allows for large ground potential differences

between systems. The receiver is equipped

with a fail-safe feature that guarantees the

receiver output will be in a HIGH state when

the input is left unconnected. The receiver of

the

SP3485 operates up to 10Mbps.

The receiver of the

SP3485 has an enable

control line which is active LOW. A logic

LOW on RE (pin 2) will enable the differential

receiver. A logic HIGH on RE (pin 2) of the

SP3485 will disable the receiver.

Low Power Shutdown Mode

Low-power shutdown mode is initiated

by bringing both RE high and DE low. In

shutdown, the devices typically draw only

50nA of supply current. RE and DE can be

drivensimultaneously;thepartisguaranteed

not to enter shutdown if RE is high and DE

is low for less than 50ns. If the inputs are in

this state for at least 600ns, the parts are

guaranteed to enter shutdown.

Enable times t

the part was not in a low-power shutdown

state. Enable times t

assume the parts were shut down. It takes

drivers and receivers longer to become

enabled from low-power shutdown mode

(t

disable mode (t

DESCRIPTION

INPUTS

OUTPUTS

RE

DE

DI

B

A

X

1

1

0

1

X

1

0

1

0

0

0

X

High-Z

1

0

X

Shutdown

INPUTS

OUTPUTS

RE

DE

V

RO

0

X

-50mV

1

0

X

-200mV

0

X

X

Open/Shorted

1

1

1

X

High-Z

1

0

X

Shutdown

Table 1. Transmit Function Truth Table

Table 2. Receive Function Truth Table