Texas Instruments SN74HCT157DRG4

Overview

SN74HCT157DRG4 from Texas Instruments is a quad 2-line-to-1-line data selector/multiplexer IC operating at 4.5 V–5.5 V, delivering ±6-mA output drive, 15 ns typical propagation delay (at 5.5 V, CL = 50 pF), and TTL-compatible inputs for digital logic routing in bus management and signal selection applications.

For engineers reviewing the SN74HCT157DRG4 datasheet, SN74HCT157DRG4 pinout, SN74HCT157DRG4 application, or SN74HCT157DRG4 equivalent, this page provides verified functional role, SOIC-16 package mapping, switching timing under load, input/output voltage thresholds, and validated alternative parts for logic-level multiplexing in industrial control and embedded interface design.

Technical Context

The SN74HCT157DRG4 implements four independent 2:1 multiplexers with a common strobe (G) and select (A/B) control, enabling simultaneous routing of two 4-bit data sources to one 4-bit output bus. Each channel features buffered inputs and outputs with defined high/low output voltage limits (VOH ≥ 3.7 V, VOL ≤ 0.33 V at IO = ±6 mA).

It uses HCMOS technology with TTL-voltage-compatible input thresholds (VIH = 2 V min, VIL = 0.8 V max), operates over −40°C to +85°C, and exhibits low quiescent current (ICC ≤ 80 µA max) while driving up to 15 LSTTL loads - making it suitable for mixed-logic interfacing without level-shifting.

Key Specifications

Pinout & Package

SN74HCT157DRG4 is packaged in a 16-pin SOIC (D package), 7.5 mm × 10.3 mm body, with 1.27 mm pitch and gull-wing leads. Pin 1 is located at the top-left corner (Q1 quadrant per tape orientation), and the package is RoHS-compliant with NiPdAu lead finish and MSL Level-1 rating.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LV157ADR and 74HC157D,653, the SN74HCT157DRG4 uniquely balances TTL input compatibility, 15-ns speed, and industrial temperature range - making it the optimal choice for retrofitting legacy 5-V logic or designing robust industrial multiplexers without level-shifting overhead.

Availability

SN74HCT157DRG4 is available at Aetrix Electronics and suitable for industrial PLC I/O expansion, microcontroller peripheral multiplexing, legacy bus interface translation, and digital test equipment signal routing requiring stable component supply and long-term manufacturability.

Supply support for SN74HCT157DRG4 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 U.S.-based semiconductor company founded in 1930, specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.

The SN74HCT157DRG4 belongs to TI's industry-standard 74HCT logic family, designed specifically to bridge TTL and CMOS logic domains with guaranteed input compatibility, predictable timing, and robust operation in harsh electrical environments.

FAQ

What is the function of the G (strobe) pin on the SN74HCT157DRG4?

The G pin on the SN74HCT157DRG4 is an active-low strobe enable that globally controls output state: when G is high, all four Y outputs are forced low regardless of A/B or input states; when G is low, outputs reflect the selected A or B inputs per the A/B control signal. This enables synchronized data gating across all four channels, critical for bus arbitration and glitch-free switching in real-time systems.

Can the SN74HCT157DRG4 operate reliably at 3.3 V?

No - the SN74HCT157DRG4 is specified only for 4.5 V to 5.5 V operation per its recommended conditions. At 3.3 V, VIH and VOH thresholds fall outside specification, resulting in undefined logic behavior and potential failure to recognize TTL inputs or drive downstream loads. For 3.3-V systems, consider SN74LV157ADR instead, which supports 2.0–5.5 V operation.

Is the SN74HCT157DRG4 pin-compatible with the SN74HC157?

Yes - the SN74HCT157DRG4 shares identical pinout, package (SOIC-16), and functional logic with SN74HC157, including matching A/B, G, and Y terminal assignments. However, SN74HCT157DRG4 accepts TTL-level inputs (VIH = 2.0 V), whereas SN74HC157 requires CMOS-level inputs (VIH = 3.5 V), so direct substitution requires verification of source logic family compatibility.

What is the maximum capacitive load the SN74HCT157DRG4 can drive while maintaining 15 ns propagation delay?

The 15 ns typical propagation delay for the SN74HCT157DRG4 is specified at CL = 50 pF and VCC = 5.5 V. As load capacitance increases to 150 pF, tpd degrades to 38 ns (max) under same conditions. To maintain ≤15 ns delay, total node capacitance - including trace, probe, and input capacitance of driven devices - must remain ≤50 pF, requiring careful PCB layout and minimal fanout.

Does the SN74HCT157DRG4 require pull-up or pull-down resistors on unused inputs?

Yes - per TI's SCBA004 application report, all unused inputs of the SN74HCT157DRG4 must be tied to VCC or GND to prevent floating states that cause increased ICC, oscillation, or ESD susceptibility. Leaving inputs unconnected risks erratic output behavior and elevated power consumption, especially in industrial environments with electromagnetic interference.