CY74FCT157CTQC 4-Bit Multiplexer Logic IC

ElecSuppliers Part Number GuideAug 22, 2026

CY74FCT157CTQC is a 4-bit multiplexer logic device from the FCT family, designed to select one of two 4-bit data sources and route the selected signals to the outputs.

The device is useful in digital systems where multiple signal sources need to share a common data path. Instead of using separate switching circuitry for every signal, a single multiplexer can control several digital lines using a common select input.

Its FCT logic architecture is designed for high-speed digital applications and can be used in computer systems, industrial controls, communication equipment and other logic-based electronic designs.

CY74FCT157CTQC Key Specifications

CY74FCT157CTQC provides four independent 2-to-1 multiplexer channels.

A common select input determines which of the two four-bit input groups is connected to the corresponding outputs. An enable control allows the entire device to be placed into its inactive state.

The device belongs to the Fairchild FCT logic family and is associated with high-speed TTL-compatible digital logic.

CY74FCT157CTQC uses a 16-pin surface-mount package, making it suitable for PCB designs where several digital logic functions need to be integrated into a relatively compact area.

4-Bit Multiplexer Operation

A multiplexer, often abbreviated as MUX, allows one of multiple input signals to be selected and routed to an output.

In the CY74FCT157 architecture, four separate data channels are controlled by the same select signal.

When the select input is changed, all four channels switch to the corresponding input group.

For example, if the select signal chooses input group A, the four outputs follow the four signals on that input group. When the select signal changes to group B, the outputs instead follow the four signals from group B.

This makes the device useful for switching parallel digital data.

CY74FCT157 Logic Architecture

CY74FCT157 belongs to the 74FCT family of fast CMOS logic devices with TTL-compatible inputs.

The architecture is intended to provide high-speed operation while maintaining relatively low power consumption compared with traditional bipolar TTL logic families.

The device can therefore be useful in systems where digital signal switching speed is important.

Its four-channel configuration also allows multiple related signals to be switched together, which can simplify system architecture and reduce the number of individual logic gates required.

CY74FCT157CTQC Applications

CY74FCT157CTQC can be used in a variety of digital logic applications.

Typical applications include data-path selection, bus switching, address or control signal routing, digital multiplexing and computer interface logic.

In an embedded system, the device can be used to allow two different peripheral sources to share a common four-bit data path.

It can also be used in industrial control systems where different logic signals need to be selected according to the operating state of the equipment.

Digital Signal Selection

One of the simplest applications for CY74FCT157CTQC is digital signal selection.

When two signal sources provide similar types of information, the multiplexer can select which source reaches the next stage of the circuit.

The common select input provides centralized control over all four channels.

This can reduce external logic requirements compared with building four separate two-input switching circuits.

For systems with multiple related digital signals, using a dedicated multiplexer can also make the schematic easier to understand.

CY74FCT157CTQC Enable Function

The multiplexer includes an enable control that determines whether the device is active.

The enable input can be used to disable the outputs when the device is not required.

This is useful in systems containing multiple logic blocks that share signal paths or buses. By controlling the enable function, designers can prevent unwanted activity from a particular multiplexer while another device is using the same system resources.

The exact output behavior and logic polarity should be verified from the device truth table when designing the circuit.

CY74FCT157CTQC Package

CY74FCT157CTQC uses a 16-pin package.

The package provides four input channels for each data group, together with the select, enable and power connections required by the logic device.

A compact surface-mount package allows the component to be integrated into dense digital PCB layouts.

When replacing the device, engineers should verify the exact package suffix because members of the 74FCT157 family may be offered in different package styles.

CY74FCT157 Replacement Considerations

When replacing CY74FCT157CTQC, the most important factors are the logic function, number of channels, input and output compatibility, supply voltage, switching characteristics and package.

A generic 74-series 4-bit multiplexer may appear functionally similar but can have different electrical characteristics.

The original FCT logic family should therefore be considered when the circuit depends on specific propagation delay, output drive capability or TTL-compatible input thresholds.

Pin compatibility should also be confirmed before selecting an alternative.

CY74FCT157CTQC in Digital Systems

The four-channel architecture makes CY74FCT157CTQC useful when several digital signals need to be switched simultaneously.

Instead of controlling each signal individually, one select signal can control all four multiplexer channels.

This is particularly useful for parallel data paths and control architectures where signals naturally occur in groups.

The device can also reduce board complexity by replacing several discrete logic gates with a single integrated circuit.

CY74FCT157CTQC for Legacy Equipment

The CY74FCT157 family is also relevant to maintenance and repair of older digital equipment.

Many industrial controllers, test instruments and computer-related systems continue to use established 74-series logic devices.

When repairing such equipment, the exact logic family can be important because older circuits may depend on specific electrical timing or drive characteristics.

For this reason, CY74FCT157CTQC should not automatically be replaced by any modern multiplexer simply because the basic Boolean function appears identical.

CY74FCT157CTQC Design Considerations

When using CY74FCT157CTQC in a new design, engineers should evaluate propagation delay, input loading, output drive capability and supply voltage.

High-speed digital switching can also generate transient currents and signal integrity issues, particularly when multiple outputs change state at the same time.

Appropriate PCB power distribution and local bypass capacitors should therefore be considered around the logic device.

Signal traces should also be routed according to the requirements of the system's operating frequency and interface environment.

CY74FCT157CTQC for Data Multiplexing

CY74FCT157CTQC provides a straightforward way to select between two four-bit digital data sources.

Its four-channel structure, common select control and enable function make it useful for digital data routing, bus selection and legacy logic designs.

For replacement applications, engineers should match the original logic family, package, pin configuration and electrical characteristics. For new designs, the required switching speed and logic-level compatibility should be evaluated before selecting the device.