Texas Instruments SN74F251BN

Overview

SN74F251BN from Texas Instruments is an 8-line-to-1-line data selector/multiplexer with 3-state complementary outputs (Y and W), designed for bus-organized digital systems. It features binary decoding of A/B/C select inputs, strobe-controlled output enable (G), and operates across 0°C to 70°C with V_CC = 4.5–5.5 V. It performs parallel-to-serial data routing in TTL-compatible logic families and supports true/inverted output delivery simultaneously.

For engineers reviewing the SN74F251BN datasheet, SN74F251BN pinout, SN74F251BN application, or SN74F251BN equivalent, this device is selected for high-speed data routing in legacy industrial control, test equipment, and microprocessor peripheral interfacing where low propagation delay (<12.5 ns), 3-state bus drive capability, and dual complementary outputs are required.

Technical Context

The SN74F251BN implements a full binary decoder driving eight input lines (D0–D7) to two complementary totem-pole outputs (Y and W), with independent 3-state control via active-low strobe (G). Its logic diagram confirms direct NAND/NOR-based selection without internal latching or clocking.

Electrical behavior is defined by TTL-compatible thresholds: V_IL ≤ 0.8 V, V_IH ≥ 2.0 V, I_OL = 24 mA (max), and I_OZL/I_OZH ≤ ±50 µA in high-impedance state. Switching performance is specified under CL = 50 pF, R1/R2 = 500 Ω, with t_PHL(D→Y) ≤ 9 ns and t_PZL(G→Y) ≤ 4.5 ns at V_CC = 5 V.

Key Specifications

Pinout & Package

SN74F251BN is supplied in a 16-pin plastic dual in-line package (PDIP-N), with 0.3-inch body width and standard through-hole pitch (0.1 inch). 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 8:1 multiplexer applications.

Compared with SN74LS251N and SN74HC251N, the SN74F251BN delivers optimal balance of speed (sub-10 ns), drive strength (24 mA), and proven TTL interoperability - making it the preferred choice for maintaining timing-critical legacy 5-V systems without redesign.

Availability

SN74F251BN is available at Aetrix Electronics and suitable for industrial control panels, test instrumentation, and educational lab equipment requiring stable component supply and long-term obsolescence management.

Supply support for SN74F251BN 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 SN74F251BN belongs to TI's 74F Fast TTL logic family, engineered for high-speed digital systems where propagation delay, drive capability, and bus interface reliability are prioritized over ultra-low power consumption.

FAQ

What is the function of the G (strobe) pin on the SN74F251BN?

The G pin is the active-low output enable (strobe) input. When G is low, the selected data appears on Y (true) and W (inverted) outputs. When G is high, both Y and W enter high-impedance state - disconnecting the SN74F251BN from the bus. This behavior is confirmed in the function table and absolute maximum ratings, where IOZH/IOZL are specified at ±50 µA.

Can the SN74F251BN be used with a 3.3-V microcontroller interface?

No - the SN74F251BN requires V_CC = 4.5–5.5 V and has TTL input thresholds (V_IH ≥ 2.0 V, V_IL ≤ 0.8 V). A 3.3-V MCU output may not reliably meet V_IH, and V_CC cannot be reduced below 4.5 V. Level-shifting circuitry is required for safe interfacing, as stated in the recommended operating conditions.

Does the SN74F251BN have internal pull-up or pull-down resistors on its inputs?

No - the SN74F251BN has no internal biasing resistors. All inputs (A, B, C, D0–D7, G) must be actively driven to valid logic levels. Floating inputs cause undefined output states and increased power consumption, as confirmed by the absence of pull-up/pull-down specs in the electrical characteristics table.

What is the maximum capacitive load the SN74F251BN can drive while maintaining specified timing?

The SN74F251BN's switching characteristics are characterized at C_L = 50 pF. Exceeding this load increases propagation delay nonlinearly and may violate setup/hold margins in synchronous systems. For loads >50 pF, buffer amplification or layout optimization (shorter traces, reduced stubs) is required per the test condition notes.

Is the SN74F251BN RoHS compliant?

Yes - the SN74F251BN is RoHS compliant, as confirmed in TI's Packaging Information Addendum, which lists "Yes" under RoHS for all active variants including SN74F251BN and SN74F251BN.A, with NIPDAU lead finish and exemption status applicable to PDIP packaging.