Datasheet

ADM3070E/ADM3071E/ADM3072E/ADM3073E/ADM3074E/ADM3075E/ADM3076E/ADM3077E/ADM3078E
Rev. E | Page 15 of 20
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 capability,
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 transceivers; 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
Table 8. Transmitting Truth Table
Transmitting Inputs Transmitting Outputs
RE
DE DI Y Z
X
1
1 1 1 0
X
1
1 0 0 1
0 0 X
1
High-Z
2
High-Z
2
1 0 X
1
Shutdown Shutdown
1
X = don't care.
2
High-Z = high impedance.
Table 9. Receiving Truth Table
Receiving Inputs Receiving Outputs
RE
DE A − B RO
0 X
1
≥ −50 mV 1
0 X
1
≤ −200 mV 0
0 X
1
Open/shorted 1
1 1 X
1
High-Z
2
1 0 X
1
Shutdown
1
X = don't care.
2
High-Z = high impedance.
ADM3071E/ADM3074E/ADM3077E
Table 10. Transmitting Truth Table
Transmitting Input Transmitting Outputs
DI Y Z
1 1 0
0 0 1
Table 11. Receiving Truth Table
Receiving Input Receiving Output
A − B RO
≥ −50 mV 1
≤ −200 mV 0
Open/shorted 1
ADM3072E/ADM3075E/ADM3078E
Table 12. Transmitting Truth Table
Transmitting Inputs Transmitting Outputs
RE
DE DI A, Y B, Z
X
1
1 1 1 0
X
1
1 0 0 1
0 0 X
1
High-Z
2
High-Z
2
1 0 X
1
Shutdown Shutdown
1
X = don't care.
2
High-Z = high impedance.
Table 13. Receiving Truth Table
Receiving Inputs Receiving Output
RE
DE A − B RO
0 0 ≥ −50 mV 1
0 0 ≤ −200 mV 0
0 0 Open/shorted 1
1 1 X
1
High-Z
2
1 0 X
1
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.