Texas Instruments CD74HCT251M

Overview

CD74HCT251M from Texas Instruments is an 8-input, three-state digital multiplexer with true (Y) and complement (Y̅) outputs, designed for bus-oriented systems. It operates at 4.5 V to 5.5 V, delivers 12 ns typical data-to-output propagation delay at 5 V/15 pF, supports –55 °C to 125 °C operation, and drives 10 LSTTL loads - enabling reliable signal routing in industrial control backplanes.

For engineers reviewing the CD74HCT251M datasheet, CD74HCT251M pinout, CD74HCT251M application, or CD74HCT251M equivalent, this device serves as a direct functional and pin-compatible replacement for the 74LS251 in 5-V TTL-compatible logic systems requiring low-power CMOS performance, bus isolation, and dual true/complement output capability.

Technical Context

The CD74HCT251M implements a silicon-gate CMOS 8:1 multiplexer with independent select inputs (S0–S2), eight data inputs (I0–I7), active-low output enable (OE), and complementary three-state outputs (Y/Y̅). Its HCT logic family ensures LSTTL input compatibility (VIL ≤ 0.8 V, VIH ≥ 2.0 V) while maintaining CMOS-level power efficiency and noise immunity (NIL/NIH = 30% of VCC).

Propagation delay is tightly controlled across temperature: data-to-Y/Y̅ tpd is 35 ns (max) over –40 °C to 85 °C and 53 ns (max) over –55 °C to 125 °C at VCC = 4.5 V; enable-to-high-Z (tdis) and enable-from-high-Z (ten) are both 30 ns (max) under same conditions - critical for synchronous bus arbitration timing.

Key Specifications

Pinout & Package

CD74HCT251M is housed in a 16-pin SOIC (D) package with nominal body size 9.90 mm × 3.90 mm, RoHS-compliant NIPDAU lead finish, and moisture sensitivity level (MSL) 1 - suitable for standard reflow assembly without dry-pack requirements.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HCT251N and 74ACT251SCX, CD74HCT251M offers optimal balance of industrial temperature range, SOIC manufacturability, and proven LSTTL interoperability - making it the preferred choice for volume production in harsh-environment embedded systems.

Availability

CD74HCT251M is available at Aetrix Electronics and suitable for industrial automation, automotive diagnostics, and aerospace subsystems requiring stable component supply across extended temperature ranges and long product lifecycles.

Supply support for CD74HCT251M 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 delivering analog, embedded processing, and logic solutions with emphasis on reliability, longevity, and industrial-grade qualification.

The CD74HCT251M belongs to TI's 74HCT logic family - engineered specifically for seamless migration from bipolar TTL to low-power CMOS in 5-V systems while preserving pin compatibility and timing behavior.

FAQ

What is the maximum operating temperature for CD74HCT251M?

The CD74HCT251M is rated for continuous operation from –55 °C to +125 °C ambient temperature. This specification is verified per TI's extended temperature testing protocol and applies to the SOIC (D) package variant. The junction temperature limit remains 150 °C, consistent with TI's absolute maximum ratings. Designers using CD74HCT251M in high-temperature enclosures should verify PCB copper pour and airflow to maintain junction temp below 150 °C under full load.

Does CD74HCT251M support true and complement outputs simultaneously?

Yes, CD74HCT251M provides both true (Y) and complement (Y̅) outputs simultaneously when enabled. These outputs reflect the selected input (I0–I7) and its logical inverse without additional delay or external components. The outputs remain in high-impedance state together when OE is high. This dual-output capability is intrinsic to the CD74HCT251M silicon design and is electrically characterized across the full temperature and voltage range.

Is CD74HCT251M pin-compatible with the 74LS251?

Yes, CD74HCT251M is functionally and pin-compatible with the 74LS251. Both devices share identical pin assignments for S0–S2, I0–I7, Y, Y̅, OE, VCC, and GND in the 16-pin SOIC package. The CD74HCT251M maintains the same truth table and timing relationships, enabling drop-in replacement in existing 5-V TTL systems - provided supply decoupling follows TI's 0.1-µF recommendation.

What is the typical propagation delay of CD74HCT251M at 5 V?

The typical propagation delay (data-to-output) for CD74HCT251M is 12 ns at VCC = 5 V, CL = 15 pF, and TA = 25 °C. This value is measured from the 50% point of the selected input transition to the 50% point of the Y or Y̅ output transition. At elevated temperatures (–40 °C to 85 °C), the maximum guaranteed tpd is 44 ns; at full industrial range (–55 °C to 125 °C), it is 53 ns - all specified in TI's SCHS169D datasheet.

Can CD74HCT251M operate below 4.5 V?

No, CD74HCT251M is not characterized or guaranteed to operate below 4.5 V. Its HCT logic family is specifically designed for 4.5 V to 5.5 V operation to ensure LSTTL input compatibility (VIH ≥ 2.0 V, VIL ≤ 0.8 V). Operation at 4.0 V or lower may result in undefined logic states, increased propagation delay, or failure to meet VIH/VIL thresholds - as confirmed by TI's Recommended Operating Conditions table in the CD74HCT251M datasheet.