NXP Semiconductors 74HCT251N,652

Overview

74HCT251N,652 from NXP Semiconductors (formerly Philips) is an 8-input CMOS multiplexer with true and complement 3-state outputs, designed for digital signal routing in TTL-compatible systems. It features propagation delays of 22–53 ns at VCC = 4.5 V, operates over −40 °C to +85 °C, and supports standard-output drive capability for bus interfacing in industrial control logic.

For engineers reviewing the 74HCT251N,652 datasheet, 74HCT251N,652 pinout, 74HCT251N,652 application, or 74HCT251N,652 equivalent, key selection criteria include 3-state output enable timing (tPZH/tPHZ ≤ 42 ns), dual Y/Y outputs for differential routing, select-input propagation delay matching, and HCT-level TTL input thresholds (VIH = 2.0 V min, VIL = 0.8 V max).

Technical Context

The 74HCT251N,652 implements a single-pole, 8-position analog/digital switch controlled by three binary select lines (S0–S2), delivering one selected input (I0–I7) to the active-low-enabled Y output while simultaneously providing its logical inverse at Y. Both outputs enter high-impedance (Z) state when OE is HIGH, enabling cascaded multiplexer architectures without external gating.

Its HCT logic family ensures compatibility with LSTTL voltage levels: inputs accept 0.8 V (VIL) and 2.0 V (VIH) thresholds, while outputs drive standard TTL loads. The device uses Si-gate CMOS technology, achieving ICC category MSI classification and supporting dynamic power calculation via CPD = 46 pF.

Key Specifications

Pinout & Package

74HCT251N,652 is supplied in a 16-pin plastic dual-in-line package (DIP) with 0.3-inch body width and through-hole mounting. Pin spacing conforms to JEDEC MS-001, and the package is RoHS-compliant per NXP's 1990–2000 era specifications.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HCT251N and 74VHC251N, the 74HCT251N,652 provides guaranteed TTL-compatible input thresholds and proven long-term reliability in fixed 5 V industrial environments, whereas SN74HCT251N offers sourcing flexibility and 74VHC251N trades compatibility for speed and voltage scalability.

Availability

74HCT251N,652 is available at Aetrix Electronics and suitable for industrial PLC I/O modules, legacy bus expansion subsystems, and educational digital logic kits requiring stable component supply and long-lifecycle support.

Supply support for 74HCT251N,652 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

NXP Semiconductors, originally Philips Semiconductors, is a global leader in high-reliability automotive, industrial, and communication ICs with deep heritage in logic families since the 1970s.

The 74HCT251N,652 belongs to the 74HCT series - a TTL-compatible CMOS logic line engineered specifically for seamless migration from 74LS designs into lower-power, higher-noise-immunity systems without board rework.

FAQ

What is the operating temperature range for the 74HCT251N,652?

The 74HCT251N,652 is specified for industrial operation from −40 °C to +85 °C. This range is confirmed in the AC characteristics tables for the 74HCT variant and aligns with JEDEC Standard No. 7A compliance. The device maintains full functionality-including propagation delay, output drive, and 3-state timing-across this entire range without derating. Its thermal performance has been validated in NXP's original 1990 datasheet under Tamb = −40 to +85 °C test conditions.

Does the 74HCT251N,652 support 3.3 V operation?

No, the 74HCT251N,652 is not rated for 3.3 V operation. Its absolute maximum VCC is 5.5 V and minimum recommended VCC is 4.5 V; operation below 4.5 V violates the HCT family's input threshold specification (VIH ≥ 2.0 V, VIL ≤ 0.8 V). At 3.3 V, input recognition becomes unreliable and output drive falls outside guaranteed limits. For 3.3 V systems, consider the 74VHC251N or level-shifted 74HCT251N,652 interfaces.

How does the 3-state enable timing affect bus arbitration in multi-mux systems?

The 74HCT251N,652's tPZH/tPHZ (13–42 ns) defines the maximum time between OE transition and Y/Y reaching valid high-impedance. In multi-mux bus architectures, this parameter ensures clean bus release before another device drives the line. For example, with 42 ns disable time and 20 MHz clocking, up to 23 such transitions fit within one clock cycle-enabling deterministic time-sliced bus sharing without contention.

Can Y and Y outputs drive complementary loads simultaneously?

Yes, both Y and Y outputs of the 74HCT251N,652 are fully buffered and electrically independent. They deliver true and complement logic levels simultaneously with matched propagation delay (≤1 ns skew typ.) and identical 3-state behavior. This allows direct connection to differential receivers, XOR gates for parity, or dual-ended transmission lines-provided load capacitance remains within CL ≤ 50 pF per output to maintain timing specs.

Is the 74HCT251N,652 pin-compatible with the 74HC251 variant?

Yes, the 74HCT251N,652 is pin-compatible with the 74HC251, sharing identical pin configuration, function table, and package outline. However, they differ in input voltage thresholds (HC: VI = GND to VCC; HCT: VI = GND to VCC−1.5 V) and propagation delay (HC is faster at 2 V but slower at 5 V). Interchange is electrically safe only if the system's input drivers meet both families' VIH/VIL requirements.