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ADM3070E/ADM3071E/ADM3072E/ADM3073E/ADM3074E/ADM3075E/ADM3076E/ADM3077E/ADM3078E
CIRCUIT DESCRIPTION
The ADM307xE series are high speed transceivers for RS-485
and RS-422 communications. Each device contains one driver
and one receiver. All devices feature fail-safe circuitry, which
guarantees a logic high receiver output when the receiver inputs
are open or shorted or when they are connected to a terminated
transmission line with all drivers disabled (see the Receiver Fail-
Safe section). The ADM307xE also feature a hot-swap capa-
bility, allowing line insertion without erroneous data transfer
(see the Hot-Swap Capability section). The ADM3070E/
ADM3071E/ADM3072E feature reduced slew rate drivers that
minimize EMI and reduce reflections caused by improperly
terminated cables, allowing for error-free data transmission at
rates up to 250 kbps.
The ADM3073E/ADM3074E/ADM3075E also offer slew rate
limits, allowing transmit speeds up to 500 kbps. The ADM3076E/
ADM3077E/ADM3078E driver slew rates are not limited,
making possible transmit speeds of up to 16 Mbps. The
ADM3072E/ADM3075E/ADM3078E are half-duplex trans-
ceivers; the ADM3070E/ADM3071E/ADM3073E/ADM3074E/
ADM3076E/ADM3077E are each full-duplex transceivers. All
devices operate from a single 3.3 V supply. Drivers are output
short-circuit current limited, and thermal shutdown circuitry
protects drivers against excessive power dissipation. When
activated, the thermal shutdown circuitry places the driver
outputs into a high impedance state.
FUNCTION TABLES
ADM3070E/ADM3073E/ADM3076E
Rev. A | Page 15 of 20
Table 8. Transmitting Truth Table
Transmitting Inputs
RE
DE
X
1
1
X
1
1
0
0
1
0
Transmitting Outputs
Y
1
0
High-Z
2
Shutdown
DI
1
0
X
1
X
1
Z
0
1
High-Z
2
Shutdown
1
X = don't care.
2
High-Z = high impedance.
Table 9. Receiving Truth Table
Receiving Inputs
RE
0
0
0
1
1
Receiving Outputs
DE
X
1
X
1
X
1
1
0
A – B
≥ 50 mV
≤ 200 mV
Open/shorted
X
1
X
1
RO
1
0
1
High-Z
2
Shutdown
1
X = don't care.
2
High-Z = high impedance.
ADM3071E/ADM3074E/ADM3077E
Table 10. Transmitting Truth Table
Transmitting Input
DI
1
0
Transmitting Outputs
Y
1
0
Z
0
1
Table 11. Receiving Truth Table
Receiving Input
A – B
≥ 50 mV
≤ 200 mV
Open/shorted
Receiving Output
RO
1
0
1
ADM3072E/ADM3075E/ADM3078E
Table 12. Transmitting Truth Table
Transmitting Inputs
RE
DE
X
1
1
X
1
1
0
0
1
0
Transmitting Outputs
DI
1
0
X
1
X
1
A, Y
1
0
High-Z
2
Shutdown
B, Z
0
1
High-Z
2
Shutdown
1
X = don't care.
2
High-Z = high impedance.
Table 13. Receiving Truth Table
Receiving Inputs
RE
DE
A – B
0
0
≥ 50 mV
0
0
≤ 200 mV
0
0
Open/shorted
1
1
X
1
1
0
X
1
Receiving Output
RO
1
0
1
High-Z
2
Shutdown
1
X = don't care.
2
High-Z = high impedance.
RECEIVER FAIL-SAFE
The ADM307xE family guarantees a logic high receiver output
when the receiver inputs are shorted, open, or connected to a
terminated transmission line with all drivers disabled. This is
done by setting the receiver input threshold between 50 mV
and 200 mV. If the differential receiver input voltage (A B) is
greater than or equal to 50 mV, RO is logic high. If A B is
less than or equal to 200 mV, RO is logic low. In the case of a
terminated bus with all transmitters disabled, the receiver
differential input voltage is pulled to 0 V by the termination.
With the receiver thresholds of the ADM307xE family, this
results in a logic high with a 50 mV minimum noise margin.