ADM3483/ADM3485/ADM3488/ADM3490/ADM3491 Data Sheet
Rev. E | Page 14 of 20
CIRCUIT DESCRIPTION
The ADM3483/ADM3485/ADM3488/ADM3490/ADM3491 are
low power transceivers for RS-485 and RS-422 communications.
The ADM3483/ADM3488 transmit and receive at data rates up
to 250 kbps; the ADM3485/ADM3490/ADM3491 transmit at up to
10 Mbps. The ADM3488/ADM3490/ADM3491 are full-duplex
transceivers, while the ADM3483/ADM3485 are half-duplex
transceivers. Driver enable (DE) and receiver enable (
RE
) pins
are included on the ADM3483/ADM3485/ADM3491. When
disabled, the driver and receiver outputs are high impedance.
DEVICES WITH RECEIVER/DRIVER ENABLES
(ADM3483/ADM3485/ADM3491)
Table 8. Transmitting Truth Table
Transmitting Input Transmitting Output
RE
DE DI B
1
A
1
Mode
X
2
1 1 0 1 Normal
X
2
1 0 1 0 Normal
0 0 X
2
High-Z
3
High-Z
3
Normal
1 0 X
2
High-Z
3
High-Z
3
Shutdown
1
A and B outputs are Y and Z, respectively, for full-duplex part (ADM3491).
2
X = don’t care.
3
High-Z = high impedance.
Table 9. Receiving Truth Table
Receiving Input Receiving Output
RE
DE
1
A – B RO
Mode
0 0 ≥ +0.2 V 1 Normal
0 0 ≤ −0.2 V 0 Normal
0 0 Inputs Open 1 Normal
1 0 X
2
High-Z
3
Shutdown
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
Table 10. Transmitting Truth Table
Transmitting Input Transmitting Output
DI Z Y
1 0 1
0 1 0
Table 11. Receiving Truth Table
Receiving Input Receiving Output
A – B RO
≥ +0.2 V 1
≤ −0.2 V 0
Inputs open 1
REDUCED EMI AND REFLECTIONS
(ADM3483/ADM3488)
The ADM3483/ADM3488 are slew rate limited transceivers,
minimizing EMI and reducing reflections caused by improperly
terminated cables.
LOW POWER SHUTDOWN MODE
(ADM3483/ADM3485/ADM3491)
A low power shutdown mode is initiated by bringing
RE
high
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 t
PSH
and t
PSL
enable times assume the part is in the
low power shutdown mode; the t
PZH
and t
PZL
enable times assume
the receiver or driver was disabled, but the part is not shut down.
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 thermal shutdown circuit forces the driver outputs
into a high impedance state if the die temperature rises
excessively.
PROPAGATION DELAY
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 (|t
PRLH
− t
PRHL
|) 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.
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.
