Texas Instruments SN74HCT157DT

Overview

SN74HCT157DT from Texas Instruments is a high-speed CMOS quad 2-line-to-1-line data selector/multiplexer with active-low enable (G), operating at 4.5 V–5.5 V supply, delivering 15 ns typical propagation delay (at 5.5 V, CL = 50 pF), ±6-mA output drive, and TTL-compatible inputs. It routes one of two 4-bit data sources to four outputs in digital control logic, commonly used in address/data bus selection and ALU input multiplexing.

For engineers reviewing the SN74HCT157DT datasheet, SN74HCT157DT pinout, SN74HCT157DT application, or SN74HCT157DT equivalent, key selection criteria include its 16-pin SOIC-D package, guaranteed 4.5–5.5 V operation, low 80-µA max ICC, buffered I/O, and compatibility with legacy TTL signal levels in mixed-voltage systems.

Technical Context

The SN74HCT157DT implements four independent 2:1 multiplexers sharing a common select (A/B) and strobe (G) input. Each Y output reflects the selected A or B input only when G is low - enabling synchronous data routing across four parallel channels without internal latching.

Its HCT logic family ensures TTL-level input thresholds (VIH = 2 V min, VIL = 0.8 V max) while maintaining CMOS power efficiency and noise immunity. All inputs are buffered, and outputs drive up to 15 LSTTL loads, supporting direct interfacing with legacy logic families without level-shifting.

Key Specifications

Pinout & Package

SN74HCT157DT is housed in a 16-pin SOIC (D) package with standard 1.27-mm pitch and 7.5-mm body width, optimized for automated assembly and thermal performance (θJA = 73°C/W).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar quad 2:1 multiplexer applications.

Compared with SN74HC157DR and 74ACT157SCX, the SN74HCT157DT uniquely balances TTL compatibility, low static power, and predictable 15-ns timing - making it optimal for industrial 5-V control logic where interoperability and reliability outweigh raw speed or ultra-low voltage operation.

Availability

SN74HCT157DT is available at Aetrix Electronics and suitable for industrial control systems, legacy equipment upgrades, and test instrumentation requiring stable component supply and long-term sourcing continuity.

Supply support for SN74HCT157DT includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a global semiconductor leader specializing in analog, embedded processing, and logic solutions, with over 90 years of innovation in industrial, automotive, and communications markets.

The SN74HCT157DT belongs to TI's HCT logic family, engineered specifically for seamless integration between TTL and CMOS systems - delivering TTL-compatible thresholds with CMOS power efficiency in standard 5-V digital control applications.

FAQ

What is the operating voltage range for the SN74HCT157DT?

The SN74HCT157DT operates over a supply voltage range of 4.5 V to 5.5 V. This tight 5-V specification ensures compatibility with standard TTL logic rails and guarantees correct input threshold behavior (VIH ≥ 2 V, VIL ≤ 0.8 V) across temperature and process variation. Operation outside this range may result in undefined logic states or increased ICC.

Does the SN74HCT157DT support true bidirectional data flow?

No, the SN74HCT157DT is a unidirectional multiplexer: data flows only from A/B inputs to Y outputs. It lacks internal tristate control per input and does not support reverse signal routing. The G (strobe) input controls output enable only - all inputs remain high-impedance receivers at all times. For bidirectional switching, discrete analog switches or dedicated bus transceivers are required.

What is the maximum capacitive load the SN74HCT157DT can drive reliably?

The SN74HCT157DT is characterized for CL = 50 pF and CL = 150 pF loads in its switching specifications. At 5.5 V, tpd increases from 15 ns (CL = 50 pF) to 19 ns (CL = 150 pF). Driving loads beyond 150 pF risks violating setup/hold timing in synchronous systems and may require local buffering - especially in high-fanout or long-trace applications.

Is the SN74HCT157DT pin-compatible with the SN74LS157?

Yes, the SN74HCT157DT shares identical pinout and function mapping with the SN74LS157, including G, A/B, A/B inputs, and Y outputs in the same 16-pin SOIC layout. However, the SN74HCT157DT draws significantly less ICC (80 µA vs. ~19 mA) and offers improved noise immunity - making it a direct drop-in replacement for LS logic in power-constrained or noise-sensitive designs.

How should unused inputs be handled on the SN74HCT157DT?

All unused inputs on the SN74HCT157DT must be tied to a valid logic level - either VCC or GND - to prevent floating nodes that cause excessive ICC, logic glitches, or ESD susceptibility. TI's application report SCBA004 explicitly warns against leaving CMOS inputs unconnected. For example, unused A/B or G pins should be pulled high via 10-kΩ resistor or hard-connected to VCC/GND depending on functional intent.