Texas Instruments SN74S157D

Overview

SN74S157D from Texas Instruments is a quadruple 2-line to 1-line data selector/multiplexer IC performing true-data routing for four independent bit channels. It features 5 ns typical propagation delay (select A/B), 20 mA low-level output drive, buffered inputs/outputs, and operates at 4.75–5.25 V over 0°C to 70°C. It is used in digital bus selection, function generation, and programmable counter control in TTL-compatible logic systems.

For engineers reviewing the SN74S157D datasheet, SN74S157D pinout, SN74S157D application, or SN74S157D equivalent, key selection criteria include propagation delay vs. power trade-off (S-series speed), true-output logic polarity, SOIC-16 package compatibility, and direct replacement feasibility within legacy 74xx multiplexer designs.

Technical Context

The SN74S157D implements four independent 2:1 multiplexers sharing a common strobe (G) and select (A/B) control. Each channel routes either input A or B to its corresponding Y output based on the A/B state, with G enabling/disabling all outputs simultaneously. All logic is positive-true and non-inverting - unlike the '158 family which inverts outputs.

It uses Schottky-clamped bipolar transistor technology to achieve high-speed operation while maintaining TTL-compatible voltage thresholds (VIH = 2 V min, VIL = 0.8 V max) and drive capability (IOL = 20 mA). The device does not include internal latching or clocking - it is purely combinational.

Key Specifications

Pinout & Package

SN74S157D is housed in a 16-pin SOIC (Small Outline Integrated Circuit) package, 3.9 mm wide, with 1.27 mm pitch and gull-wing leads. Pin 1 is marked by a beveled corner or dot; the package is RoHS-compliant with green (no Sb/Br) finish and CU/Ni/Pd/Au lead finish.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar multiplexer applications.

Compared with SN74LS157D and SN74HC157DR, the SN74S157D delivers the fastest propagation delay and highest output drive in the 74xx multiplexer family, making it optimal for timing-critical bus arbitration and high-fan-out legacy TTL systems - at the cost of higher static power and stricter supply regulation.

Availability

SN74S157D is available at Aetrix Electronics and suitable for bus selection, digital function generation, and programmable counter control requiring stable component supply across industrial control, test equipment, and legacy system upgrades.

Supply support for SN74S157D 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 ICs with broad industrial and automotive qualification.

The SN74S157D belongs to TI's legacy 74S TTL logic family, designed specifically for high-speed digital systems requiring faster performance than standard or LS TTL while maintaining pin compatibility and interface consistency.

FAQ

What is the maximum operating frequency supported by the SN74S157D?

The SN74S157D is a combinational logic device with no internal clock, so it does not have a specified maximum operating frequency. Its usable data rate depends on propagation delay (5 ns typical A/B→Y) and system setup/hold timing. In practice, it reliably supports data switching up to ~100 MHz in well-designed PCB layouts with proper termination and decoupling.

Can the SN74S157D be used as a direct replacement for the SN74LS157D on an existing PCB?

Yes, the SN74S157D is pin-compatible and functionally identical to the SN74LS157D in terms of logic behavior, pin assignment, and package (SOIC-16). However, SN74S157D draws more supply current (195 mW vs. 49 mW) and has faster edges, so verify thermal margins and signal integrity - especially on long traces or unterminated lines - before substitution.

Does the SN74S157D support 3.3 V logic levels?

No, the SN74S157D is a 5 V-only TTL device. Its input thresholds (VIH ≥ 2 V, VIL ≤ 0.8 V) and output voltages (VOH ≈ 2.7 V min, VOL ≈ 0.5 V max at 20 mA) are specified only for VCC = 4.75–5.25 V. It is not guaranteed to operate correctly with 3.3 V inputs or outputs and lacks 3.3 V tolerance.

What is the purpose of the strobe (G) pin on the SN74S157D?

The strobe (G) pin on the SN74S157D is an active-low enable that globally controls all four Y outputs. When G is low, outputs reflect the selected A/B inputs; when G is high, all Y outputs enter a high-impedance (Hi-Z) state. This allows multiple SN74S157D devices to share a common bus without external tri-state logic.

Is the SN74S157D RoHS compliant and lead-free?

Yes, the SN74S157D is RoHS compliant and lead-free. Per TI's packaging documentation, the SOIC-16 variant uses green (RoHS & no Sb/Br) materials with Cu/Ni/Pd/Au lead finish and meets JEDEC Level-1 moisture sensitivity requirements.