7 Detailed Description

7.1 Overview

The SN74LVC244A contains 8 individual high speed CMOS buffers organized as two 4-bit buffers/line drives

with 3-state outputs.

Each buffer performs the boolean logic function xYn = xAn, with x being the bank number and n being the

channel number.

Each output enable (xOE) controls four buffers. When the xOE pin is in the low state, the outputs of all buffers

in the bank x are enabled. When the xOE pin is in the high state, the outputs of all buffers in the bank x are

disabled. All disabled output are placed into the high-impedance state.

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

pull-up resistor; the minimum value of the resistor is determined by the current sinking capability of the driver and

the leakage of the pin as defined in the Electrical Characteristics table.

7.2 Functional Block Diagram

xA2

xA3

xA4

One of Two 4-Bit Bus Buffers

xA1

xOE

xY1

xY2

xY3

xY4

Figure 7-1. Logic Diagram (Positive Logic)

7.3 Feature Description

7.3.1 Balanced CMOS 3-State Outputs

This device includes balanced CMOS 3-state outputs. Driving high, driving low, and high impedance are the

three states that these outputs can be in. 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 can drive 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.

When placed into the high-impedance state, the output will neither source nor sink current, with the exception of

minor leakage current as defined in the Electrical Characteristics table. In the high-impedance state, the output

voltage is not controlled by the device and is dependent on external factors. If no other drivers are connected

to the node, then this is known as a floating node and the voltage is unknown. A pull-up or pull-down resistor

can be connected to the output to provide a known voltage at the output while it is in the high-impedance state.

The value of the resistor will depend on multiple factors, including parasitic capacitance and power consumption

limitations. Typically, a 10kΩ resistor can be used to meet these requirements.

Unused 3-state CMOS outputs should be left disconnected.

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SN74LVC244A

SCAS414AE – NOVEMBER 1992 – REVISED AUGUST 2025

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