74151

74151 8-Line to 1-Line Data Selector/Multiplexer

Overview

The 74151 is a high-speed TTL (Transistor-Transistor Logic) integrated circuit that functions as an 8-line to 1-line data selector/multiplexer. It is designed to select one of eight binary data inputs and route it to a single output line based on a 3-bit select input. This component is widely used in digital systems for data routing, signal gating, and parallel-to-serial conversion applications. The 74151 offers high-speed operation, making it suitable for performance-critical systems.

Features

• High-Speed Operation: Typical propagation delay of 15ns at 5V.
• Wide Operating Voltage Range: 4.75V to 5.25V.
• Eight Data Inputs: Can select from eight independent data lines (D0-D7).
• Three Select Inputs (A, B, C): Binary-encoded selection of one of eight inputs.
• Complementary Outputs: Provides both true (Y) and inverted (W) outputs.
• Strobe Input (G): Active-low enable input for output control.
• TTL-Compatible: Fully compatible with standard TTL logic levels.
• Low Power Consumption: Typical ICC of 32mA at 5V.

Applications

• Data Routing: Selection of one data line from multiple sources.
• Parallel-to-Serial Conversion: Used in serial communication systems.
• Function Generation: Can implement combinational logic functions.
• Memory Addressing: Used in memory systems for address decoding.
• Signal Multiplexing: Combining multiple signals onto a single line.
• Digital Systems: General purpose digital logic applications.

Electrical Characteristics

The following table summarizes the key electrical characteristics of the 74151 at VCC = 5V and TA = 25°C:

• Supply Voltage (VCC): 4.75V to 5.25V
• Input High Voltage (VIH): Min 2.0V
• Input Low Voltage (VIL): Max 0.8V
• Output High Voltage (VOH): Min 2.4V at IOH = -400μA
• Output Low Voltage (VOL): Max 0.4V at IOL = 16mA
• Input Clamp Voltage (VIK): Max -1.5V at IIK = -18mA
• Supply Current (ICC): Max 32mA
• Propagation Delay (tPLH, tPHL): 15ns typical, 22ns max
• Power Dissipation (PD): 160mW max

Functional Description

The 74151 operates as an 8-input digital multiplexer. The three select inputs (A, B, C) form a 3-bit binary number that determines which of the eight data inputs (D0-D7) is connected to the output. The active-low strobe input (G) enables the device when low and forces both outputs to logic low when high.

The device provides both true (Y) and complementary (W) outputs. When enabled (G = LOW), the Y output follows the selected data input while the W output provides its complement. This complementary output feature can be useful in certain logic implementations.

Truth Table

The following truth table describes the operation of the 74151:

• G = 1: Y = 0, W = 1 (regardless of other inputs)
• G = 0: Y = Dn, W = Dn' (where n is the decimal equivalent of CBA)

Package Information

The 74151 is available in several package options:

• 16-pin DIP (Dual In-line Package): Most common through-hole package
• 16-pin SOIC (Small Outline IC): Surface mount version
• 16-pin TSSOP (Thin Shrink Small Outline Package): Smaller footprint surface mount option

Pin configuration for the standard 16-pin DIP package:

• Pin 1: D3
• Pin 2: D2
• Pin 3: D1
• Pin 4: D0
• Pin 5: Y (Output)
• Pin 6: W (Complementary Output)
• Pin 7: G (Strobe Input, active low)
• Pin 8: GND
• Pin 9: C (Select Input)
• Pin 10: B (Select Input)
• Pin 11: A (Select Input)
• Pin 12: D7
• Pin 13: D6
• Pin 14: D5
• Pin 15: D4
• Pin 16: VCC

Design Considerations

When using the 74151 in circuit designs, consider the following:

• Power Supply Decoupling: Use a 0.1μF ceramic capacitor close to the VCC pin.
• Unused Inputs: Tie unused data inputs to either VCC or GND as required.
• Output Loading: Do not exceed maximum fan-out specifications (10 standard TTL loads).
• Propagation Delay: Account for timing delays in critical path designs.
• Temperature Considerations: Electrical characteristics may vary with temperature.

Alternative Components

For applications requiring different features or technologies, consider these alternatives:

• 74LS151: Lower power Schottky version
• 74HC151: CMOS version with wider voltage range
• CD4051: Analog/digital multiplexer with similar functionality
• 74F151: Faster version with reduced propagation delay

Conclusion

The 74151 remains a versatile and reliable component for digital multiplexing applications despite being introduced decades ago. Its high-speed operation, complementary outputs, and straightforward interface make it suitable for a wide range of digital system designs. When properly implemented with attention to its electrical characteristics and package requirements, the 74151 can provide robust performance in data selection and routing applications.