Texas Instruments SN74LS157D

Overview

SN74LS157D from Texas Instruments is a quad 2-line to 1-line data selector/multiplexer in a 16-pin SOIC package, operating over 0°C to 70°C, with typical propagation delay of 15 ns at V_CC = 5 V and I_OL = 8 mA, used for digital signal routing in TTL-compatible logic systems.

For engineers reviewing the SN74LS157D datasheet, SN74LS157D pinout, SN74LS157D application, or SN74LS157D equivalent, key selection considerations include its quad 2:1 multiplexing function, TTL-level input thresholds, complementary enable control (G̅), and compatibility with legacy 74LS logic families in industrial control and instrumentation interfaces.

Technical Context

The SN74LS157D implements four independent 2-input multiplexers sharing a common strobe (G̅) and select (S) control line, enabling simultaneous routing of four bit-pairs based on a single address bit. Its internal architecture uses standard TTL bipolar transistor logic with Schottky-clamped outputs to suppress saturation delay.

It features active-low enable (G̅) that forces all Y outputs high-impedance when asserted, and a non-inverting select (S) that routes A inputs to Y when low and B inputs to Y when high. Input thresholds are defined per TTL specifications: V_IL ≤ 0.8 V, V_IH ≥ 2.0 V.

Key Specifications

Pinout & Package

SN74LS157D is housed in a 16-pin SOIC (D) package with 1.27 mm pitch, 7.5 mm body width, and 2.00 mm max height. Pin 1 is located at the top-left corner with notch or dot marking.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS157D, SN74LS157N offers mechanical compatibility with legacy through-hole designs, while SN74LS157DR provides RoHS compliance and optimized packaging for high-volume SMT manufacturing - neither alters logic behavior or timing, making both drop-in replacements in their respective assembly contexts.

Availability

SN74LS157D is available at Aetrix Electronics and suitable for industrial control panels, legacy instrumentation interfaces, and educational electronics kits requiring stable component supply and long-term obsolescence management.

Supply support for SN74LS157D 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 and embedded processing technologies with broad industrial, automotive, and consumer product portfolios.

The SN74LS157D belongs to TI's legacy 74LS logic family, designed specifically for TTL-compatible digital systems requiring reliable, low-cost, discrete logic functions in commercial temperature environments.

FAQ

What is the primary function of the SN74LS157D?

The SN74LS157D is a quad 2-line to 1-line data selector/multiplexer. It routes four independent bit-pairs (A1–A4 and B1–B4) to corresponding outputs (Y1–Y4) based on a shared select (S) input and enabled by an active-low strobe (G̅). This allows synchronized selection of one of two 4-bit data sources in TTL-level digital systems, making it ideal for address decoding, bus switching, and signal routing tasks where minimal control lines are preferred.

Is the SN74LS157D pin-compatible with other 74LS multiplexers like the SN74LS158?

No, the SN74LS157D is not pin-compatible with the SN74LS158. While both are quad multiplexers in 16-pin packages, the SN74LS158 is a quad 2-line to 1-line multiplexer with inverted outputs (Y̅), whereas the SN74LS157D provides true (non-inverted) outputs. Their pin assignments differ significantly - for example, SN74LS158 places its select input on pin 15 but uses pin 6 for G̅, unlike SN74LS157D's G̅ on pin 1. Direct substitution would require PCB redesign.

Can the SN74LS157D operate at 3.3 V?

No, the SN74LS157D is not specified for 3.3 V operation. It is designed for 5 V ±5% (4.75 V to 5.25 V) TTL supply rails. Operating below 4.75 V may cause marginal logic thresholds, increased propagation delay, or failure to meet output drive specifications. For 3.3 V systems, consider modern alternatives such as the SN74LVC157A, which is functionally equivalent but 3.3 V compatible.

What does the "D" suffix indicate in SN74LS157D?

The "D" suffix in SN74LS157D denotes the SOIC (Small Outline Integrated Circuit) package type - a 16-pin surface-mount package with 1.27 mm lead pitch and 7.5 mm body width. This distinguishes it from other variants like SN74LS157N (PDIP), SN74LS157NSR (SOP), or military-grade SN54LS157J (CDIP). The "D" package supports automated SMT assembly and offers higher board density than through-hole options.

Does the SN74LS157D support hot swapping or live insertion?

No, the SN74LS157D does not support hot swapping. It lacks built-in protection against supply sequencing, ESD stress during insertion, or back-drive current from live buses. Applying power or signals before V_CC is stable may cause latch-up or parametric degradation. Always power-cycle the board before inserting or removing the SN74LS157D, and ensure proper decoupling and grounding to prevent transient-induced failures.