7 Detailed Description

7.1 Overview

The SNx4ACT240 devices are organized as two 4-bit buffers or drivers with separate output-enable (OE) inputs.

When OE is low, the device passes inverted data from the A inputs to the Y outputs. When OE is high, the

outputs are in the high-impedance state.

To put the device in the high-impedance state during power up or power down, tie OE to VCC through a pullup

resistor; the current-sinking capability of the driver determines the minimum value of the resistor.

7.2 Functional Block Diagram

Figure 7-1. Logic Diagram (Positive Logic)

7.3 Feature Description

7.3.1 Balanced CMOS Push-Pull Outputs

This device includes balanced CMOS push-pull outputs. The term balanced indicates that the device can sink

and source similar currents. The drive capability of this device may create fast edges into light loads, so routing

and load conditions should be considered to prevent ringing. Additionally, the outputs of this device are capable

of driving larger currents than the device can sustain without being damaged. It is important for the output power

of the device to be limited to avoid damage due to overcurrent. The electrical and thermal limits defined in the

Absolute Maximum Ratings must be followed at all times.

Unused push-pull CMOS outputs should be left disconnected.

7.4 Device Functional Modes

Table 7-1. Function Table (Each Buffer)

INPUTS

OUTPUT

OE

A

Y

L

H

L

L

L

H

H

X

Z

SN54ACT240, SN74ACT240

SCAS515E – JUNE 1995 – REVISED NOVEMBER 2023

www.ti.com

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