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DS1487
Low Power RS-485 1/4 Unit Load Multipoint Transceiver
DS1487
Low Power RS-4851⁄4 Unit Load Multipoint Transceiver
General DescriptionThe DS1487isa low-power transceiverfor RS-485 and
RS-422 communication.The device containsone driverand
one receiver.The drivers slew rateallowsfor operationupto
2.0 Mbps (see Applications Information section). The trans-
ceiver presents 1⁄4unitloadingto theRS-485 busallowingup128 nodestobe connected together withouttheuseofre-
peaters.
The transceiver draws 200μAof supply current whenun-
loadedor fully loaded withthe driver disabledand operates
froma single +5V supply.
The driveris short-circuit current limited andis protected
against excessive power dissipationby thermal shutdown
circuitry that placesthe driver outputs into TRI-STATE®
(High Impedance state) under fault conditions. The driver
guaranteesa minimumof 1.5V differential output voltage
with maximum loading acrossthe common mode range
(VOD3).
The receiver hasa failsafe feature that guaranteesa
logic-high outputifthe inputis open circuit.
The DS1487is availablein surface mountand DIP pack-
ages.
Features Meets TIA/EIA RS-485 multipoint standard Allowsupto128 transceiversonthebus(1⁄4 U.L.) Guaranteedfull load output voltage (VOD3) Low quiescent current: 200 μAtyp −7Vto +12V common-mode input voltage range TRI-STATE outputson driverand receiverAC performance: Driver transition time:25nstyp Driver propagation delay:40nstyp Driver skew:1nstyp Receiver propagation delay: 200nstyp Receiver skew:20nstyp Half-duplex flow through pinout Operates froma single5V supply Current-limitingand thermal shutdownfor driver
overload protectionPinand functional compatible with MAX1487
Connection and Logic Diagram
Order Number Temp. Range Package/###DS1487N 0˚Cto +70˚C DIP/N08E
DS1487M 0˚Cto +70˚C SOP/M08A
Truth Table
DRIVER SECTION(Note1)
DI A B HHH L L L H
XLX ZZ
RECEIVER SECTION(Note1)
A-B RO ≥+0.2V H ≤−0.2V L X Z L OPEN (Note1) H= indeterminate= TRI-STATE
Note1: NonTerminated, OpenInputonly
TRI-STATE®isa registeredtrademark ofNationalSemiconductorCorporation.
DIP and SOICDS012920-1
*Note:NonTerminated, OpenInputonly
July 1998
DS1487
Low
Power
RS-485
Unit
Load
Multipoint
ransceiver 1999 National Semiconductor Corporation DS012920
