ADM3483/ADM3485/ADM3488/ADM3490/ADM3491
CIRCUIT DESCRIPTION
The ADM3483/ADM3485/ADM3488/ADM3490/ADM3491
REDUCED EMI AND REFLECTIONS—
ADM3483/ADM3488
are low power transceivers for RS-485 and RS-422 communi-
cations. The ADM3483/ADM3488 transmit and receive at data
rates up to 250 kbps; the ADM3485/ADM3490/ADM3491 trans-
mit at up to 10 Mbps. The ADM3488/ADM3490/ADM3491 are
full-duplex transceivers, while the ADM3483/ADM3485 are half-
The ADM3483/ADM3488 are slew rate limited transceivers,
minimizing EMI and reducing reflections caused by improp-
erly terminated cables.
duplex transceivers. Driver enable (DE) and receiver enable (
)
RE
LOW POWER SHUTDOWN MODE
pins are included on the ADM3483/ADM3485/ADM3491. When
disabled, the driver and receiver outputs are high impedance.
(ADM3483/ADM3485/ADM3491)
A low power shutdown mode is initiated by bringing
high
RE
DEVICES WITH RECEIVER/DRIVER ENABLES—
ADM3483/ADM3485/ADM3491
and DE low. The devices do not shut down unless both the driver
and receiver are disabled (high impedance). In shutdown mode,
the devices typically draw only 2 nA of supply current. For these
devices, the tPSH and tPSL enable times assume the part is in the
low power shutdown mode; the tPZH and tPZL enable times assume
the receiver or driver was disabled, but the part is not shut down.
Table 8. Transmitting Truth Table
Transmitting Input
Transmitting Output
RE
DE
DI
B1
A1
Mode
X2
X2
0
1
1
0
0
1
0
X2
X2
0
1
1
0
Normal
Normal
Normal
Shutdown
DRIVER OUTPUT PROTECTION
Two methods are implemented to prevent excessive output
current and power dissipation caused by faults or by bus
contention. Current limit protection on the output stage
provides immediate protection against short circuits over
the whole common-mode voltage range (see the Typical
Performance Characteristics section). In addition, a ther-
mal shutdown circuit forces the driver outputs into a high
impedance state if the die temperature rises excessively.
High-Z3
High-Z3
High-Z3
High-Z3
1
1 A and B outputs are Z and Y respectively, for full-duplex part (ADM3491).
2 X = don’t care.
3 High-Z = high impedance.
Table 9. Receiving Truth Table
Receiving Input
DE1
Receiving Output
RO
RE
A – B
Mode
PROPAGATION DELAY
0
0
0
1
0
0
0
0
≥ +0.2 V
≤ −0.2 V
Inputs Open
X2
1
0
1
Normal
Normal
Normal
Shutdown
Skew time is the difference between the low-to-high and high-
to-low propagation delays. Small driver/receiver skew times help
maintain a symmetrical mark-space ratio (50% duty cycle).
The receiver skew time (|tPRLH − tPRHL|) is under 10 ns (20 ns
for ADM3483/ADM3488). The driver skew times are 8 ns for
ADM3485/ADM3490/ADM3491 and typically under 100 ns for
ADM3483/ADM3488.
High-Z3
1 DE is a don’t care; X for the full-duplex part (ADM3491).
2 X = don’t care.
3 High-Z = high impedance.
DEVICES WITHOUT RECEIVER/DRIVER ENABLES—
ADM3488/ADM3490
TYPICAL APPLICATIONS
The ADM3483/ADM3485/ADM3491 transceivers are designed
for half-duplex bidirectional data communications on multipoint
bus transmission lines, Figure 32 and Figure 33 show typical
network applications circuits. The ADM3488 and the ADM3490
full-duplex transceivers are designed to be used in a daisy-chain
network topology or in a point-to-point application, see Figure 34
and Figure 35. The ADM3491 can be used as line repeat Figure 36.
To minimize reflections, the line must be terminated at both
ends in its characteristic impedance, and stub lengths off the main
line must be kept as short as possible. The slew rate limited
ADM3483/ADM3488 are more tolerant of imperfect termination.
Table 10. Transmitting Truth Table
Transmitting Input
Transmitting Output
DI
1
0
Z
0
1
Y
1
0
Table 11. Receiving Truth Table
Receiving Input
A – B
Receiving Output
RO
1
≥ +0.2 V
≤ −0.2 V
0
Inputs open
1
Rev. B | Page 14 of 20
ADI [ ADI ]
