STMicroelectronics M74HC251B1R

Overview

M74HC251B1R from STMicroelectronics is a high-speed CMOS 8-channel 3-state multiplexer with true (Y) and complementary (W) outputs, STROBE-enabled output control, symmetrical 4 mA drive capability, 17 ns typical propagation delay at 6 V, and operation across 2–6 V supply. It routes one of eight digital inputs to dual outputs under 3-bit address control (A/B/C), used in data routing, bus isolation, and logic-level signal selection in industrial control panels.

For engineers reviewing the M74HC251B1R datasheet, M74HC251B1R pinout, M74HC251B1R application, or M74HC251B1R equivalent, key selection criteria include 3-state enable timing (tPZL/tPLZ), input noise immunity (28% VCC), balanced tPLH/tPHL delays, and DIP-16 compatibility with legacy 74-series designs.

Technical Context

The device implements a single-pole, 8-throw analog/digital multiplexer function using silicon gate C2MOS technology, with independent STROBE-controlled 3-state outputs on Y and W pins. Its logic diagram confirms full decoding of A/B/C select lines and direct gating of D0–D7 inputs without internal latching or clocking.

All inputs feature integrated ESD protection diodes, and output impedance is matched for |IOH| = |IOL| ≥ 4 mA, enabling bidirectional signal integrity in shared-bus architectures. Propagation delays are specified separately for data-to-output (D→Y/W) and address-to-output (A/B/C→Y/W) paths, supporting timing-critical address decoding and data switching.

Key Specifications

Pinout & Package

Package: Plastic DIP-16 (0.300" width), JEDEC MS-001, body dimensions 20.0 × 8.5 mm, lead pitch 2.54 mm.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 8-channel 3-state multiplexer applications.

Compared with SN74HC251N and 74VHC251N, M74HC251B1R provides superior low-power operation (4 µA vs. ≥8 µA), wider temperature coverage (−55°C to +125°C), and higher noise immunity-making it optimal for mission-critical industrial and automotive signal routing where reliability trumps raw speed.

Availability

M74HC251B1R is available at Aetrix Electronics and suitable for industrial PLC I/O expansion, automotive sensor multiplexing, and legacy test equipment signal switching requiring stable component supply across long production lifecycles.

Supply support for M74HC251B1R 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, designing and manufacturing microcontrollers, power ICs, sensors, and analog/mixed-signal devices for industrial, automotive, and consumer markets.

M74HC251B1R belongs to the M74HC high-speed CMOS logic family, engineered for pin- and function-compatible upgrades of legacy 74LS/74F logic in harsh-environment applications demanding wide VCC range and extended temperature operation.

FAQ

What is the maximum recommended operating frequency for M74HC251B1R in a 5 V system?

The device supports reliable operation up to 30 MHz in 5 V systems, based on its 17 ns typical propagation delay and 13 ns max tPLH/tPHL at VCC = 4.5 V. For sustained 50% duty-cycle square-wave routing, ensure input rise/fall times ≤500 ns and load capacitance ≤50 pF to maintain timing margins per AC specifications.

Does M74HC251B1R require external pull-up resistors on Y or W outputs?

No. The Y and W outputs are actively driven in both logic states and present high-impedance only when STROBE is high. Pull-ups are unnecessary unless interfacing with open-drain receivers or implementing wired-OR logic - in which case a 10 kΩ resistor to VCC is sufficient for leakage compensation.

Can STROBE be tied permanently low to disable 3-state functionality?

Yes. Holding STROBE low continuously enables Y/W outputs at all times, converting the device into a non-inverting/complementing 8:1 multiplexer. This configuration is valid across the full −55°C to +125°C range and does not affect propagation delay or drive strength specifications.

Is M74HC251B1R RoHS-compliant and halogen-free?

Yes. Per STMicroelectronics' official product change notice (PCN 19-0127), M74HC251B1R in DIP-16 packaging conforms to RoHS Directive 2011/65/EU and is certified halogen-free (Cl < 900 ppm, Br < 900 ppm, total halogens < 1500 ppm), with exemption 7a for lead in high-melting-temperature solder alloys.