Texas Instruments SN74LS251NE4

Overview

SN74LS251NE4 from Texas Instruments is a dual 4-line to 1-line data selector/multiplexer with three-state outputs, implemented in TTL logic, operating over 0°C to 70°C, featuring 16-pin PDIP package, propagation delay of 22 ns (max) at V_CC = 5 V, and output drive capability of ±8 mA. It enables digital signal routing in bus-oriented systems such as address/data multiplexing in microprocessor peripherals.

For engineers reviewing the SN74LS251NE4 datasheet, SN74LS251NE4 pinout, SN74LS251NE4 application, or SN74LS251NE4 equivalent, key selection criteria include its 3-state output enable control, dual independent 4:1 select paths, TTL-compatible input thresholds, and compatibility with legacy 74LS-family timing and voltage margins.

Technical Context

The SN74LS251NE4 integrates two independent 4-input multiplexers sharing common select lines (S0–S2) and individual output enable (1G̅, 2G̅), each driving a three-state output (1Y, 2Y). Its internal architecture uses standard TTL bipolar transistors with Schottky clamping for speed optimization.

Logic operation follows Boolean equations: 1Y = G̅ · Σ m_i · D_i, where m_i are minterms selected by S2S1S0, and D₀–D₃ are data inputs. Output high/low voltage levels meet TTL specifications: V_OH ≥ 2.7 V (I_OH = –0.4 mA), V_OL ≤ 0.5 V (I_OL = 8 mA).

Key Specifications

Pinout & Package

SN74LS251NE4 is housed in a 16-pin plastic dual in-line package (PDIP-N), 0.300-inch wide body, with 0.100-inch lead pitch and through-hole mounting. Pin 1 is located at the top-left corner, identified by a notch or dot marking on the package.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS153N and SN74HC153N, the SN74LS251NE4 uniquely combines dual 4:1 selection with per-channel 3-state control in a TTL-compatible package - making it the only option among the three that supports direct, contention-free bus interfacing without external logic.

Availability

SN74LS251NE4 is available at Aetrix Electronics and suitable for microprocessor bus multiplexing, industrial control logic, test equipment signal routing, and educational lab platforms requiring stable component supply and long-term obsolescence management.

Supply support for SN74LS251NE4 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 reach.

The SN74LS251NE4 belongs to TI's legacy 74LS logic family, designed specifically for backward-compatible upgrades of TTL-based digital systems requiring reliable, low-cost, through-hole multiplexing functionality.

FAQ

What is the primary function of the SN74LS251NE4?

The SN74LS251NE4 is a dual 4-line to 1-line data selector/multiplexer with independent three-state outputs. It routes one of four digital inputs per channel to a single output based on binary-select inputs S0–S2, and each output can be enabled or disabled via dedicated active-low enable pins (1G̅ and 2G̅). This makes the SN74LS251NE4 especially useful in bus-oriented architectures where signal isolation and shared-line control are required.

Does the SN74LS251NE4 support 3.3 V logic interfaces?

No, the SN74LS251NE4 is a 5 V-only TTL device with specified operation from 4.75 V to 5.25 V. Its input thresholds (V_IH ≥ 2.0 V, V_IL ≤ 0.8 V) and output drive characteristics are optimized for 5 V TTL signaling. Direct interface with 3.3 V logic may cause unreliable switching or excessive current draw; level-shifting circuitry is required for mixed-voltage systems involving the SN74LS251NE4.

Can the SN74LS251NE4 replace the SN74LS153 in an existing design?

The SN74LS251NE4 cannot serve as a direct drop-in replacement for the SN74LS153 because it includes three-state outputs (controlled by 1G̅ and 2G̅), whereas the SN74LS153 has permanently enabled outputs. If the original design relies on always-active outputs or lacks enable logic, substituting the SN74LS251NE4 would require modifying control signals and verifying bus contention behavior. The SN74LS251NE4 offers enhanced flexibility but demands updated system-level enable coordination.

What is the maximum clock frequency supported by the SN74LS251NE4?

The SN74LS251NE4 does not contain an internal clock; it is a purely combinatorial device. Its usable maximum switching rate depends on propagation delay (22 ns max) and system setup/hold timing. In practice, it reliably supports address/data multiplexing in 8-bit microprocessor systems running up to 20 MHz, provided select inputs are stable before data transitions. The SN74LS251NE4 performance is governed by external timing constraints, not an internal oscillator.

Is the SN74LS251NE4 RoHS compliant?

Yes, the SN74LS251NE4 is RoHS compliant, with lead finish specified as NiPdAu (nickel-palladium-gold) and marked "Yes" in TI's official packaging documentation. It meets EU Directive 2011/65/EU requirements and is suitable for environmentally regulated commercial electronics manufacturing where lead-free assembly is mandated.