ADM483E
Rev. A | Page 11 of 16
GENERAL INFORMATION
The ADM483E is a robust RS-485 transceiver that operates
from a single 5 V supply.
It is ideally suited for operation in electrically harsh environ-
ments or where cables may be plugged and unplugged. It is also
immune to high RF field strengths without special shielding
precautions. The ADM483E is intended for balanced data
transmission and complies with both EIA Standards RS-485 and
RS-422. It contains a differential line driver and a differential
line receiver; it is suitable for half-duplex data transmission
because 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 has 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 components
such as transorbs or surge suppressors.
Low electromagnetic emissions are achieved using slew limited
drivers, minimizing interference both conducted and radiated.
The ADM483E can transmit at data rates up to 250 kbps.
A typical application for the ADM483E is illustrated in
Figure 23.
This figure 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
because the slew rate is controlled by the ADM483E and
reflections are minimized.
The communications network can be extended to include
multipoint connections as shown in
Figure 26. Up to 32
transceivers can be connected to the bus.
E384MDAE384MDA
RS-485/RS-422 LINK
RO
DI
DE
DI
DE
B
A
GND
B
A
GND
RO
0.1µF0.1µF
+5
+5
V
CC
V
CC
RE
RE
06012-023
Figure 23. Typical Half-Duplex Link Application
Tabl e 6 and Table 7 show the truth tables for transmitting and
receiving.
Table 6. Transmitting Truth Table
Inputs Outputs
RE
DE DI B A
X
1
1 1 0 1
X
1
1 0 1 0
0 0 X
1
High-Z High-Z
1 0 X
1
High-Z High-Z
1
X = don’t care.
Table 7. Receiving Truth Table
Inputs Outputs
RE
DE A − B RO
0 0 ≥ +0.2 V 1
0 0 ≤ −0.2 V 0
0 0 Inputs O/C 1
1 0 X
1
High-Z
1
X = don’t care.
ESD TRANSIENT PROTECTION SCHEME
The ADM483E uses protective clamping structures on its inputs
and outputs that clamp the voltage to a safe level and dissipate
the energy present in ESD (electrostatic discharge).
The protection structure achieves ESD protection up to ±15 kV
according to the Human Body Model.
