Texas Instruments SN74HC251DG4

Overview

SN74HC251DG4 from Texas Instruments is an 8-to-1 data selector/multiplexer with complementary 3-state outputs, full binary decoding, and strobe-controlled enable logic. It operates from 2 V to 6 V, delivers ±6 mA output drive at 5 V, exhibits typical propagation delay of 9 ns (VCC = 4.5 V, CL = 50 pF), and supports parallel-to-serial conversion in bus-interfaced digital systems.

For engineers reviewing the SN74HC251DG4 datasheet, SN74HC251DG4 pinout, SN74HC251DG4 application, or SN74HC251DG4 equivalent, this device serves as a drop-in 3-state multiplexer for address/data routing, serial interface generation, and logic-level signal selection where low power (80 μA max ICC), high noise immunity, and bus-compatible drive capability are required.

Technical Context

The SN74HC251DG4 implements full 3-bit binary decoding (A/B/C inputs) to select one of eight data inputs (D0–D7), routing it to complementary 3-state outputs Y (true) and W (inverted). Output-enable (OE) controls both outputs simultaneously, placing them in high-impedance state when asserted high.

Its CMOS HC-family architecture ensures rail-to-rail input compatibility, low input current (≤1 μA), and robust switching performance across temperature (−40°C to +85°C) and supply voltage (2–6 V). The device meets standard TTL load drive requirements-capable of directly driving up to 15 LSTTL loads.

Key Specifications

Pinout & Package

SN74HC251DG4 is housed in a 16-pin SOIC (D) package measuring 9.90 mm × 3.90 mm, with standard 1.27 mm pitch and gull-wing leads. Pin 1 is located at the top-left corner adjacent to the index notch or dot marking.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 8-to-1 multiplexer applications.

Compared with SN74HC151DR, SN74HC251DG4 adds essential complementary outputs for dual-rail signaling; versus 74LVC151PW, it trades speed for wider voltage flexibility and SOIC compatibility - making SN74HC251DG4 optimal for industrial retrofits and mixed-supply environments.

Availability

SN74HC251DG4 is available at Aetrix Electronics and suitable for industrial control systems, test equipment signal routing, microcontroller peripheral expansion, and legacy bus interface translation requiring stable component supply and long-term obsolescence management.

Supply support for SN74HC251DG4 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 logic ICs, with decades of heritage in industry-standard logic families including the 74HC series.

SN74HC251DG4 belongs to TI's 74HC high-speed CMOS logic product line, engineered for reliable 8-channel data selection in industrial, automotive, and communications systems where wide voltage operation and bus compatibility are critical.

FAQ

What is the function of the W output on the SN74HC251DG4?

The W output on the SN74HC251DG4 provides a logically inverted copy of the selected data input (D0–D7), synchronized with the true Y output. This complementary pair enables direct connection to differential receivers, clock-domain crossing circuits, or logic that requires both polarities without adding external inverters - a key differentiator from the SN74HC151DR, which lacks W. Both outputs are simultaneously enabled or disabled by OE.

Does SN74HC251DG4 support 3.3 V operation?

Yes, SN74HC251DG4 fully supports 3.3 V operation within its specified 2 V to 6 V supply range. At VCC = 3.3 V, it maintains guaranteed logic thresholds (VIH ≥ 2.0 V, VIL ≤ 0.99 V), delivers ≥±4 mA output drive, and achieves typical tpd of ~12 ns (CL = 50 pF), making it suitable for mixed-voltage systems interfacing with 3.3 V microcontrollers while retaining compatibility with legacy 5 V peripherals.

Is SN74HC251DG4 pin-compatible with SN74HC151?

Yes, SN74HC251DG4 is pin-compatible with SN74HC151 in the same SOIC-16 package (D), sharing identical pin assignments for A, B, C, D0–D7, OE, Y, VCC, and GND. The only physical difference is that SN74HC251DG4 exposes the W (inverted) output on pin 15, whereas SN74HC151 leaves that pin unconnected - allowing drop-in replacement when W functionality is not required.

What is the maximum capacitive load SN74HC251DG4 can drive reliably?

SN74HC251DG4 is characterized for CL = 50 pF and CL = 150 pF in its switching specifications. At 5 V supply, it maintains tpd ≤ 65 ns and output transition time (tt) ≤ 16 ns even at 150 pF, confirming robust drive capability for typical PCB traces and multiple gate inputs. For loads exceeding 150 pF, TI recommends verifying timing margins in the target application, as excessive capacitance may degrade edge rates and increase propagation delay beyond spec limits.

How should unused inputs be handled on SN74HC251DG4?

All unused address (A/B/C) and data (D0–D7) inputs on SN74HC251DG4 must be tied to a valid logic level - either VCC or GND - to prevent floating nodes that cause increased ICC, erratic switching, or ESD susceptibility. TI explicitly states in the datasheet that unused inputs must not be left open; tying to VCC is preferred for D inputs if default-high behavior is acceptable, while A/B/C may be grounded to force selection of D0 when inactive.