MC34058 MC34059

7

MOTOROLA ANALOG IC DEVICE DATA

Table 1. Driver Truth Table

Enables

Outputs

Driver Data Inputs

DEX

REX

OAX

OBX

H

H

H

H

L

L

H

H

L

H

X

L

H

Z

Z

X

H

L

Not Defined

Not Defined

The outputs will be in a high impedance state when:

a) The Enable inputs are set according to Table 1;

b) The junction temperature exceeds the trip point of the thermal shutdown circuit. When in this condition, the output’s source and sink capability are shut off, and a

leakage current of less than 20

µA will flow. Disabled outputs may be taken to any voltage between –7.0 V and 12 V without damage to internal circuitry.

The drivers are protected from short circuits by two methods:

a) Current limiting is provided at each output, in both the source and sink direction, for shorts to any voltage within the 12 V to –7.0 V range, with respect to circuit

ground. The short circuit current will flow until the fault is removed, or until the thermal shutdown activates. The current limiting circuit has a negative temperature

coefficient and requires no resetting upon removal of the fault condition.

b) A thermal shutdown circuit disables the outputs when the junction temperature reaches +150

°C, ± 20°C. The thermal shutdown circuit has a hysteresis of ∼ 12°C

to prevent oscillations. When this circuit activates, the output stage of each driver is put into the high impedance mode, thereby shutting off the output currents.

However, the remainder of the internal circuitry remains biased and the outputs will become active once again as the IC cools down.

Receiver Inputs

The receiver inputs and enable logic determine the state of

the receiver outputs in accordance with Table 2. Each

receiver input pair has a nominal differential threshold of at

most 200 mV (Pin OAX with respect to OBX) and a common

mode voltage range of –7.0 V and 12 V must be maintained

for proper operation. A nominal hysteresis of 100 mV is

typical. The receiver input characteristics are shown in

Figure 8. When the inputs are in the high impedance state,

they remain capable of the common mode voltage range of

–7.0 V to 12 V.

Receiver Outputs

The receiver outputs are TTL type outputs and act in

accordance with Table 2.

Enable Logic

Each driver output is active when the Driver Enable input

is true according to Table 1. Each receiver output is active

when the Receiver Enable input is true according to Table 2.

The Enable inputs have a nominal threshold of 1.2 V and

their voltage must be kept within the range of 0 V and VCC for

proper operation. If the voltage is taken more than 0.5 V

below ground or above VCC, excessive currents will flow and

proper operation of the drivers will be affected. An open pin is

equivalent to a logic high, but good design practices dictate

that inputs should never be left open. The enable inputs are

TTL compatible. Since the same pins are used for driver input

and receiver output, care must be taken to make sure that

DEX and REX are not both enabled. This may result in

corruption of both the transmitted and received data.

Table 2. Receiver Truth Table

Receiver Data Inputs

Enables

Outputs

OAX–OBX

DEX

REX

DRX

≥ +200 mV

L

L

H

≤ –200 mV

L

L

L

X

L

H

Z

X

H

L

Not Defined

APPLICATIONS

The MC34058/9 was designed to meet EIA/TIA–422 and

EIA/TIA–485 standards. EIA/TIA–422 specifies balanced

point–to–point transmission with the provision for multiple

receivers on the line. EIA/TIA–485 specifies balanced

point–to–point transmission and allows for multiple drivers

and receivers on the line. Refer to EIA/TIA documents for

more details. Figure 9 shows a typical EIA/TIA–422 example.

Figure 10 shows a typical EIA/TIA–485 example.

Figure 9. Typical EIA/TIA–422 Application

RT

100

Ω