ADM3483E/ADM3486E/ADM3488E/ADM3490E/ADM3491E
CIRCUIT DESCRIPTION
The ADM34xxE are low power transceivers for RS-485 and RS422
communications. The ADM3483E/ADM3488E operate at data
rates up to 250 kbps. The ADM3486E operates at data rates up
to 2.5 Mbps, and the ADM3490E/ADM3491E transmit at up to
12 Mbps. The ADM3488E/ADM3490E/ADM3491E are full-
duplex transceivers, and the ADM3483E/ADM3486E are half
duplex. Driver enable (DE) and receiver enable (RE) pins are
included on the ADM3483E/ADM3486E/ADM3491E. When
disabled, the driver and receiver outputs are high impedance.
Table 12. Receiving Truth Table
Receiving Input
A–B
≥ +0.2 V
≤ −0.2 V
Inputs open
Receiving Output
RO
1
0
1
LOW POWER SHUTDOWN MODE—ADM3483E/
ADM3486E/ADM3491E
The ADM3483E/ADM3486E/ADM3491E are put into a low
power shutdown mode by bringing both RE high and DE low.
The devices do not shut down unless both the driver and the
receiver are disabled (high impedance). In shutdown mode, the
devices typically draw less than 1 μA of supply current. For
these devices, the t
PSH
and the t
PSL
enable times assume the part
was in the low power shutdown mode; the t
PZH
and the t
PZL
enable times assume the receiver or the driver was disabled, but
the part was not shut down.
DEVICES WITH RECEIVER/DRIVER ENABLE—
ADM3483E/ADM3486E/ADM3491E
Table 9. Transmitting Truth Table
Transmitting Inputs
DE
DI
RE
0
1
1
Transmitting Outputs
1
0
High-Z
High-Z
0
1
High-Z
High-Z
1
1
0
0
1
0
Mode
Normal
Normal
Normal
Shutdown
ADM3483E and ADM3486E only.
2
ADM3491E only.
3
X = don’t care.
4
High-Z = high impedance.
DRIVER OUTPUT PROTECTION
The ADM34xxE family implements two ways to prevent
excessive output current and power dissipation caused by faults
or by bus contention. A current limit on the output stage
provides immediate protection against short circuits over the
whole common-mode voltage range (see the Typical
shutdown circuit forces the driver outputs into a high
impedance state if the die temperature rises excessively.
Table 10. Receiving Truth Table
RE
0
0
0
1
1
Receiving Inputs
DE
DE
A – B
0
0
0
0
Receiving Output
RO
1
0
1
High-Z
≥ +0.2 V
≤ −0.2 V
Inputs open
Mode
Normal
Normal
Normal
Shutdown
PROPAGATION DELAY
propagation delays. Skew time is simply the difference between
the low-to-high and the high-to-low propagation delays. Small
driver/receiver skew times help maintain a symmetrical mark-
space ratio (50% duty cycle).
The receiver skew time, |t
PRHL
– t
PRHL
|, is under 10 ns (20 ns for
the ADM3483E/ADM3488E). The driver skew time is 8 ns for
the ADM3490E/ADM3491E, 12 ns for the ADM3486E, and
typically under 50 ns for the ADM3483E/ADM3488E.
ADM3483E and ADM3486E only.
2
ADM3491E only.
3
X = don’t care.
4
High-Z = high impedance.
DEVICES WITHOUT RECEIVER/DRIVER ENABLE―
ADM3488E/ADM3490E
Table 11. Transmitting Truth Table
Transmitting Input
DI
1
0
Z
0
1
Transmitting Outputs
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, Figure 34 illustrates an
example of a line repeater.
Rev. A | Page 14 of 20
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