ADM3483/ADM3485/ADM3488/ADM3490
CIRCUIT DESCRIPTION
The ADM3483/ADM3485/ADM 3488/ADM3490 are low-
power transceivers for RS-485 and RS-422 communications.
The ADM3483 and ADM3488 can transmit and receive at data
rates up to 250kbps, and the ADM3485/ ADM3490 at up to
10Mbps. The ADM3488/ ADM3490 are full-duplex
transceivers, while the ADM3483/ADM3485 are half-duplex.
Driver Enable (DE) and Receiver Enable (RE) pins are included
on the ADM3483/ADM3485. When disabled, the driver and
receiver outputs are high impedance.
Preliminary Technical Data
REDUCED EMI AND REFLECTIONS
(ADM3483/ ADM3488)
The ADM3483/ADM3488 are slew-rate limited, minimizing
EMI and reducing reflections caused by improperly terminated
cables.
LOW-POWER SHUTDOWN MODE
(ADM3483/ADM3485)
A low-power shutdown mode is initiated by bringing both
RE
high and DE low. The devices will not shut down unless both
the driver and receiver are disabled (high impedance). In
shutdown, the devices typically draw only 2nA of supply
current. For these devices, the t
PSH
and t
PSL
enable times assume
the part was in the low-power shutdown mode; the t
PZH
and t
PZL
enable times assume the receiver or driver was disabled, but the
part was not shut down.
DEVICES WITH RECEIVER/DRIVER ENABLES
(ADM3483/ADM2485)
RE
X
X
0
1
Inputs
DE
1
1
0
0
DI
1
0
X
X
Outputs
B*
A*
0
1
1
0
High-Z
High-Z
High-Z
High-Z
Mode
Normal
Normal
Normal
Shutdown
DRIVER OUTPUT PROTECTION
Excessive output current and power dissipation caused by faults
or by bus contention are prevented by two methods. A foldback
current limit on the output stage provides immediate protection
against short circuits over the whole common-mode voltage
range (see Typical Performance Characteristics). In addition, a
thermal shutdown circuit forces the driver outputs into a high-
impedance state if the die temperature rises excessively.
Table x. Transmitting Truth Table
RE
0
0
0
1
Inputs
DE
A,B
0*
≥+0.2V
0*
≤-0.2V
0*
Inputs Open
0
x
Outputs
RO
1
0
1
High-Z
Mode
Normal
Normal
Normal
Shutdown
PROPAGATION DELAY
Skew time is simply the difference between the low-to-high and
high-to-low propagation delay. Small driver/receiver skew times
help maintain a symmetrical mark-space ratio (50% duty cycle).
The receiver skew time, |tPRLH - tPRHL|, is under 10ns (20ns
for the ADM3483/ADM3488). The driver skew times are 8ns
for the ADM485/ADM3490, and typically under 100ns for the
ADM3483/ADM3488.
Table x. Receiving Truth Table
DEVICES WITHOUT RECEIVER/DRIVER ENABLES
(ADM3488/ADM2490)
Input
DI
1
0
Outputs
Z
0
1
Y
1
0
LINE LENGTH VS. DATA RATE
The RS-485/RS-422 standard covers line lengths up to 4000 feet.
For line lengths greater than 4000 feet, see Figure 13.
TYPICAL APPLICATIONS
The ADM3483, ADM3485, ADM3488 and ADM3490
transceivers are designed for bidirectional data communications
on multipoint bus transmission lines. Figures 11 and 12 show
typical network applications circuits. These parts can also be
used as line repeaters, with cable lengths longer than 4000 feet,
as shown in Figure 13. To minimize reflections, the line should
be terminated at both ends in its characteristic impedance, and
stub lengths off the main line should be kept as short as
possible. The slew-rate-limited ADM3483/ADM3488 are more
tolerant of imperfect termination.
Table x. Transmitting Truth Table
Input
A,B
≥+0.2
≤
-0.2
Inputs Open
Outputs
RO
0
1
1
Table x. Receiving Truth Table
Rev.PrD | Page 12 of 14
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