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DS1487

Low Power RS-485

⁄

Unit Load Multipoint Transceiver

General Description

The DS1487 is a low-power transceiver for RS-485 and

RS-422 communication. The device contains one driver and

one receiver. The drivers slew rate allows for operation up to

2.0 Mbps (see Applications Information section). The trans-

ceiver presents

⁄

unit loading to the RS-485 bus allowing up

to 128 nodes to be connected together without the use of re-

peaters.

The transceiver draws 200 µA of supply current when un-

loaded or fully loaded with the driver disabled and operates

from a single +5V supply.

The driver is short-circuit current limited and is protected

against excessive power dissipation by thermal shutdown

circuitry that places the driver outputs into TRI-STATE

(High Impedance state) under fault conditions. The driver

guarantees a minimum of 1.5V differential output voltage

with maximum loading across the common mode range

OD3

The receiver has a failsafe feature that guarantees a

logic-high output if the input is open circuit.

The DS1487 is available in surface mount and DIP pack-

ages.

Features

n Meets TIA/EIA RS-485 multipoint standard

n Allows up to 128 transceivers on the bus (

⁄

U.L.)

n Guaranteed full load output voltage (V

OD3

)

n Low quiescent current: 200 µA typ

n −7V to +12V common-mode input voltage range

n TRI-STATE outputs on driver and receiver

n AC performance:

— Driver transition time: 25 ns typ

— Driver propagation delay: 40 ns typ

— Driver skew: 1 ns typ

— Receiver propagation delay: 200 ns typ

— Receiver skew: 20 ns typ

n Half-duplex flow through pinout

n Operates from a single 5V supply

n Current-limiting and thermal shutdown for driver

overload protection

n Pin and functional compatible with MAX1487

Connection and Logic Diagram

Order Number Temp. Range Package/

###

DS1487N 0˚C to +70˚C DIP/N08E

DS1487M 0˚C to +70˚C SOP/M08A

Truth Table

DRIVER SECTION

(Note 1)

DE DI A B

XHHHL

XHLLH

XLXZZ

RECEIVER SECTION

(Note 1)

DE A-B RO

LL ≥+0.2V H

LL ≤−0.2V L

HX X Z

L L OPEN (Note 1) H

X = indeterminate

Z = TRI-STATE

Note 1: Non Terminated, Open Input only

TRI-STATE

is a registered trademark of National Semiconductor Corporation.

DIP and SOIC

DS012920-1

*Note: Non Terminated, Open Input only

July 1998

DS1487 Low Power RS-485

⁄

Unit Load Multipoint Transceiver