Texas Instruments CD54HCT251F3A

Overview

CD54HCT251F3A from Texas Instruments is a military-grade 8-input CMOS multiplexer with three-state outputs, true/complement outputs (Y/Y̅), and output enable (OE) control. It operates at 4.5–5.5 V, delivers 12 ns typical data-to-output propagation delay at 5 V/15 pF/25 °C, drives 10 LSTTL loads, and supports –55 °C to +125 °C operation in bus-oriented digital systems.

For engineers reviewing the CD54HCT251F3A datasheet, CD54HCT251F3A pinout, CD54HCT251F3A application, or CD54HCT251F3A equivalent, this page provides verified functional identity, military-qualified thermal and timing specs, bus-interface design guidance, and validated drop-in alternatives for high-reliability embedded and defense electronics.

Technical Context

The CD54HCT251F3A implements an 8:1 digital multiplexer using silicon-gate CMOS technology with TTL-compatible input thresholds (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V) and CMOS-level output drive. Its three-state outputs support bidirectional bus arbitration, while simultaneous true (Y) and complement (Y̅) outputs enable differential signaling or logic redundancy without external inverters.

It features full military-grade operating temperature range (–55 °C to +125 °C), absolute maximum ratings up to 7 V supply, and robust ESD protection per MIL-STD-883. The device is functionally and pin-compatible with the 74LS251, enabling direct replacement in legacy LSTTL-based systems requiring enhanced noise immunity and reduced power.

Key Specifications

Pinout & Package

CD54HCT251F3A uses a 16-pin Ceramic Dual In-line Package (CDIP-J) with 24.38 mm × 6.92 mm body size, hermetically sealed for military reliability and moisture resistance. Pin 1 is located at the top-left corner when viewed from the top with notch or dot orientation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 8-input multiplexer applications.

Compared with CD54HC251F3A, the CD54HCT251F3A offers guaranteed TTL input compatibility and faster speed at 5 V, while SN74LS251N provides higher drive strength but lacks three-state and complement outputs - making CD54HCT251F3A the optimal balance of interoperability, bus efficiency, and military reliability.

Availability

CD54HCT251F3A is available at Aetrix Electronics and suitable for avionics data routing, secure crypto I/O switching, radar calibration path selection, and automated test equipment channel management requiring stable component supply across extended temperature and lifecycle requirements.

Supply support for CD54HCT251F3A 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 global semiconductor leader specializing in analog, embedded processing, and high-reliability logic solutions with over 50 years of aerospace and defense component qualification experience.

The CD54HCT251F3A belongs to TI's military-grade HCT logic family, designed specifically for drop-in replacement of legacy TTL in harsh-environment systems requiring extended temperature operation, hermetic packaging, and MIL-PRF-38535 compliance.

FAQ

What is the supply voltage range for CD54HCT251F3A?

The CD54HCT251F3A operates strictly within 4.5 V to 5.5 V. Operation outside this range violates recommended conditions and may cause unreliable switching or accelerated parametric drift. This narrow window ensures precise TTL-compatible input threshold behavior and stable CMOS output drive across its full –55 °C to +125 °C military temperature range. Always use a regulated 5 V source with local 0.1 µF ceramic bypassing per TI layout guidelines.

Does CD54HCT251F3A support true and complement outputs simultaneously?

Yes, CD54HCT251F3A provides both true (Y) and complement (Y̅) outputs on separate pins (14 and 15). These outputs reflect the selected input (I0–I7) and its logical inverse simultaneously when OE is low. This dual-output architecture eliminates the need for external inverters in applications requiring differential signaling, parity generation, or redundant path monitoring - a key differentiator from standard 74LS251.

Is CD54HCT251F3A pin-compatible with the 74LS251?

Yes, CD54HCT251F3A is functionally and pin-compatible with the 74LS251. All 16 pins match in position, signal name, and electrical behavior - including identical S0–S2 select inputs, I0–I7 data inputs, OE control, Y output, and V_CC/GND. This enables direct replacement in existing designs to gain lower power, higher noise immunity, and extended temperature operation without PCB modification.

What is the maximum propagation delay for CD54HCT251F3A at full temperature range?

The maximum data-to-output propagation delay (t_pd) for CD54HCT251F3A is 53 ns over –55 °C to +125 °C at V_CC = 4.5 V and C_L = 50 pF. At the more common 5 V/15 pF condition, typical delay is 12 ns with a guaranteed max of 44 ns. This performance enables reliable operation in systems with >10 MHz multiplexed clock domains and real-time signal routing requirements.

How does the three-state output of CD54HCT251F3A behave during OE high?

When OE is high, both Y and Y̅ outputs enter high-impedance (Z) state with leakage current ≤ ±5.0 µA across –55 °C to +125 °C. This isolates the device from the bus, preventing signal contention in multi-driver configurations. The transition times from active to high-Z (t_PZH/t_PLZ) are guaranteed ≤ 45 ns max, ensuring clean bus release without glitches - critical for synchronous bus arbitration in avionics and defense systems.