Texas Instruments SN74LS157DR

Overview

SN74LS157DR from Texas Instruments is a quad 2-line-to-1-line data selector/multiplexer in a 16-pin SOIC package, operating from 4.75 V to 5.25 V with typical propagation delay of 15 ns at V_CC = 5 V and T_A = 25 °C, supporting TTL-compatible inputs and outputs for digital logic routing in industrial control and instrumentation systems.

For engineers reviewing the SN74LS157DR datasheet, SN74LS157DR pinout, SN74LS157DR application, or SN74LS157DR equivalent, key selection criteria include its 4-channel 2:1 multiplexing function, guaranteed fan-out of 20 LS-TTL loads, input clamp diodes for transient protection, and commercial temperature range (0 °C to 70 °C) compliance.

Technical Context

The SN74LS157DR implements four independent 2-input multiplexers sharing a common strobe (G̅) and select (S) control line, enabling synchronous routing of two 4-bit data buses. Its TTL-compatible input thresholds (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V) and output drive capability (I_OH = –0.4 mA, I_OL = 8 mA) ensure interoperability with legacy 74LS logic families.

Internally, it uses bipolar Schottky transistor technology to achieve stable switching performance across its full operating voltage (4.75–5.25 V) and temperature (0–70 °C) range, with no internal latching or clocked operation - all outputs respond combinatorially to S and G̅ states.

Key Specifications

Pinout & Package

SN74LS157DR is housed in a 16-pin Small Outline Integrated Circuit (SOIC) package (Package Drawing D), 7.5 mm wide, with 1.27 mm pitch, RoHS-compliant NiPdAu lead finish, and moisture sensitivity level (MSL) 1 (unlimited floor life at ≤30 °C/60% RH).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS157DR, SN74LS158DR delivers inverted outputs with identical timing and pinout - useful for complementing logic but requiring downstream inversion handling; SN74HC157DR offers CMOS efficiency and supply flexibility but lacks native LS-TTL interoperability and clamp protection, necessitating careful signal integrity validation.

Availability

SN74LS157DR is available at Aetrix Electronics and suitable for industrial control, test equipment, and legacy microprocessor system design requiring stable component supply, long-term obsolescence management, and RoHS-compliant sourcing.

Supply support for SN74LS157DR 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, automotive, and consumer market reach.

The SN74LS157DR belongs to TI's legacy 74LS logic family, designed specifically for reliable, pin-compatible replacement of earlier TTL multiplexers in cost-sensitive, medium-speed digital systems.

FAQ

What is the maximum clock frequency supported by SN74LS157DR?

The SN74LS157DR is a purely combinatorial device with no internal clock - it does not operate at a "clock frequency." Its usable data switching rate is limited by propagation delay (15 ns max) and system setup/hold timing. In practice, SN74LS157DR reliably supports asynchronous data routing up to approximately 30 MHz in well-designed PCB layouts with proper termination and decoupling.

Does SN74LS157DR support 3.3 V logic interfacing?

No, SN74LS157DR is a 5 V-only TTL device. Its input thresholds (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V) and output levels (V_OH ≈ 2.7 V min at I_OH = –0.4 mA) are incompatible with 3.3 V CMOS logic without level translation. Direct connection to 3.3 V systems may cause unreliable switching or excessive input current; use SN74LVC157 or similar 3.3 V–tolerant alternatives instead.

Can SN74LS157DR outputs drive LEDs directly?

Yes - each SN74LS157DR output can sink up to 8 mA (I_OL), sufficient to drive standard 2 mA–5 mA indicator LEDs with appropriate series resistors (e.g., 330 Ω at 5 V). However, do not exceed total package I_CC limits (60 mA typical) when lighting multiple LEDs simultaneously, and avoid sourcing current (I_OH = –0.4 mA) for LED anode connections.

Is SN74LS157DR pin-compatible with SN74LS158DR?

Yes - SN74LS157DR and SN74LS158DR share identical 16-pin SOIC (D) packaging, pin assignments, and electrical timing. The sole functional difference is output polarity: SN74LS157DR provides true (non-inverted) outputs, while SN74LS158DR provides complementary (inverted) outputs. No PCB layout change is needed for substitution, but logic-level inversion must be accounted for in downstream circuitry.

What is the purpose of the G̅ (strobe) pin on SN74LS157DR?

The G̅ (active-low strobe) pin on SN74LS157DR enables global output enable/disable control: when G̅ = HIGH, all four Y outputs enter high-impedance (Hi-Z) state regardless of S or input values; when G̅ = LOW, outputs respond normally to S and data inputs. This allows SN74LS157DR to share a common bus or prevent signal contention during system reset or power sequencing.