ADM3070E/ADM3071E/ADM3072E/ADM3073E/ADM3074E/ADM3075E/ADM3076E/ADM3077E/ADM3078E

Rev. F | Page 15 of 20

CIRCUIT DESCRIPTION

The ADM307xE series are high speed transceivers for RS­485

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

X1

1

1

1

0

X1

1

0

0

1

0

0

X1

High-Z2

High-Z2

1

0

X1

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

X1

≥ −50 mV

1

0

X1

≤ −200 mV

0

0

X1

Open/shorted

1

1

1

X1

High-Z2

1

0

X1

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

X1

1

1

1

0

X1

1

0

0

1

0

0

X1

High-Z2

High-Z2

1

0

X1

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

X1

High-Z2

1

0

X1

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.