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ADM1487AR

Ultra-Low Power RS-485/RS-422 Transceiver with Low EMI and +/-10kV ESD Protection

Analog Devices 

ADM1487

PRELIMINARY TECHNICAL DATA

CMOS outout stages, which include parasitic diodes from

their driver outputs to each supply rail and can latch up

when these diodes conduct.

VCC

SCHOTTKY

R E V E R S E -B IA S E D

WHEN OUTPUT

> VCC+VD

PARASITIC

DIODE DP

PARASITIC

DIODE DP

SCHOTTKY

R E V E R S E -B IA S E D

WHEN OUTPUT

< GND - VD

Figure 9. ADM1487 Driver Output Stage

The ADM1487 output includes Schottky diodes in series

with the positive supply to the drain of the P-channel output

device and in series with the drain of the N-channel output

device. These diodes prevent the P-channel's parasitic diode

from conducting when the output voltage exceeds VCC and

prevent the N-channel's parasitic diode from conducting

when the output voltage falls below ground.

SLEW RATE CONTROL

The driver output stage of the ADM1487 has a controlled

slew rate to minmize signal reflections on incorrectly termi-

nated lines and to reduce electromagnetic interference (EMI).

CURRENT LIMIT AND THERMAL SHUTDOWN

The ADM1487 incorporates two protection mechanisms to

guard the drivers against short-circuits, bus contention or

other fault conditions. The first is a current-limited output

stage that protects the driver against short-circuits over the

entire common-mode voltage range by limiting the output

current to about 70mA. Under extreme fault condtions

where the current limit is not effective, a thermal shutdown

circuit puts the driver outputs into a high-impedance state if

the die temperature exceeds 150°C, and does not turn them

back on until the temperature has fallen to 130°C.

ENHANCED ESD PROTECTION

All Analog Devices parts incorporate protection against

electrostatic discharge (ESD) to protect the devices dur-

ing handling, assembly and normal operation. In addition,

the ADM1487 has enhanced ESD protection up to ±10kV

on the A and B I/O pins to protect against severe opera-

tional conditions such as line transients, connection and

disconnection.

APPLICATION INFORMATION

Figure 10 shows a typical application of the ADM1487.

This is a half-duplex RS-485/RS-422 network. Up to 254

additional ADM1487s can be connected along the cable

(termination resistors are only required at each end).

+5V

RECEIVER

OUTPUT

1

(RO)

RECEIVER

ENABLE

2

DRI(VREER)

3

R

8

7B

RT

6

100n (VCC

)

CABLE TERMINATED

AT ENDS

5

6

RT

7

D

4

DI

3

DE

2

RE

ENABLE

A

DA(DTEA)

4

D

5

IN (DI)

+5V (VCC) 8

R

B A B A 100n

1

RO

ADM1487

ADDITIONAL

ADM1487s

ADM1487

Figure 10. Typical Half-Duplex RS-485/RS-422 Network

OUTLINE DIMENSIONS

Dimensions shown in inches and (mm).

8-Pin Plastic Dual-In-Line Package (N-8)

8-Pin SO Package (R-8)

0.430 (10.92)

0.348 (8.84)

8

5

0.280 (7.11)

0.240 (6.10)

14

0.325 (8.25)

PIN 1

0.060 (1.52)

0.300 (7.62)

0.210 (5.33)

0.015 (0.38)

MAX

0.130

0.160 (4.06)

0.115 (2.93)

(3.30)

MIN

0.022 (0.558) 0.100 0.070 (1.77)

0.014 (0.356) (2.54) 0.045 (1.15)

BSC

SE A TIN G

PLANE

0.195 (4.95)

0.115 (2.93)

0.015 (0.381)

0.008 (0.204)

0.1968 (5.00)

0.1890 (4.80)

85

0.244 0 (6.20)

0.228 4 (5.80) 1

0.1574 (4.00)

4 0.1497 (3.80)

PIN 1

0.102 (2.59)

0.094 (2.39)

0.0196 (0.50)

x 45

0.0099 (0.25)

0.009 8 (0 .25)

0.004 0 (0 .10)

8

0.0500 0.0192 (0.49)

0

SE A TIN G (1.27) 0.0138 (0.35) 0.0098 (0.25)

PLANE BSC

0.0075 (0.19)

0.05 00 (1 .27)

0.01 60 (0 .41)

–8–

Rev. PrC

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