ADM483E
GENERAL INFORMATION
The ADM483E is a ruggedized RS-485 transceiver that operates
from a single +5 V supply.
It contains protection against radiated and conducted interfer-
ence, including high levels of electrostatic discharge.
It is ideally suited for operation in electrically harsh environ-
ments or where cables may be plugged/unplugged. It is also
immune to high RF field strengths without special shielding
precautions. It is intended for balanced data transmission and
complies with both EIA Standards RS-485 and RS-422. It con-
tains a differential line driver and a differential line receiver, and
is suitable for half duplex data transmission as the driver and
receiver share the same differential pins.
The input impedance on the ADM483E is 12 kΩ, allowing up to
32 transceivers on the differential bus.
The ADM483E operates from a single +5 V
±
10% power
supply. Excessive power dissipation caused by bus contention or
by output shorting is prevented by a thermal shutdown circuit.
This feature forces the driver output into a high impedance state
if, during fault conditions, a significant temperature increase is
detected in the internal driver circuitry.
The receiver contains a fail-safe feature that results in a logic
high output state if the inputs are unconnected (floating).
A high level of robustness is achieved using internal protection
circuitry, eliminating the need for external protection compo-
nents such as tranzorbs or surge suppressors.
Low electromagnetic emissions are achieved using slew limited
drivers, minimizing interference both conducted and radiated.
The ADM483 can transmit at data rates up to 250 kbps.
A typical application for the ADM483E is illustrated in Figure
20. This shows a half-duplex link where data may be transferred
at rates up to 250 kbps. A terminating resistor is shown at both
ends of the link. This termination is not critical since the slew
rate is controlled by the ADM483E and reflections are minimized.
The communications network may be extended to include
multipoint connections as shown in Figure 30. Up to 32
transceivers may be connected to the bus.
+5V
0.1µF
+5V
0.1µF
Tables II and III show the truth tables for transmitting and
receiving.
Table II. Transmitting Truth Table
Inputs
RE
X
X
0
1
X = Don’t Care.
Outputs
DE
1
1
0
0
DI
1
0
X
X
B
0
1
Hi-Z
Hi-Z
A
1
0
Hi-Z
Hi-Z
Table III. Receiving Truth Table
Inputs
RE
0
0
0
1
X = Don’t Care.
Outputs
DE
0
0
0
0
A-B
≥
+0.2 V
≤
–0.2 V
Inputs O/C
X
RO
1
0
1
Hi-Z
ESD/EFT TRANSIENT PROTECTION SCHEME
The ADM483E uses protective clamping structures on its
inputs and outputs that clamp the voltage to a safe level and
dissipates the energy present in ESD (Electrostatic) and EFT
(Electrical Fast Transients) discharges.
The protection structure achieves ESD protection up to
±
15 kV
according to the Human Body Model, and EFT protection up
to
±
2 kV on all I-O lines.
ESD TESTING
Two coupling methods are used for ESD testing, contact
discharge and air-gap discharge. Contact discharge calls for a
direct connection to the unit being tested. Air-gap discharge
uses a higher test voltage but does not make direct contact with
the unit under test. With air discharge, the discharge gun is
moved toward the unit under test, developing an arc across the
air gap, hence the term air-discharge. This method is influenced
by humidity, temperature, barometric pressure, distance and
rate of closure of the discharge gun. The contact-discharge
method, while less realistic, is more repeatable and is gaining
acceptance and preference over the air-gap method.
Although very little energy is contained within an ESD pulse,
the extremely fast rise time, coupled with high voltages, can
cause failures in unprotected semiconductors. Catastrophic
destruction can occur immediately as a result of arcing or
heating. Even if catastrophic failure does not occur immedi-
ately, the device may suffer from parametric degradation, which
may result in degraded performance. The cumulative effects of
continuous exposure can eventually lead to complete failure.
HIGH
VOLTAGE
GENERATOR
R2
C1
DEVICE
UNDER TEST
R2
1.5K
C1
100pF
RE
RO
V
CC
V
CC
DE
DI
B
B
A
RS485/RS-422 LINK
RO
ADM483E
DI
DE
A
ADM483E
GND
GND
RE
Figure 20. Typical Half-Duplex Link Application
ESD Test Method
Human Body Model
Figure 21. ESD Generator
–6–
REV. 0
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