Texas Instruments SN74HC251NSR

Overview

SN74HC251NSR from Texas Instruments is an 8-to-1 data selector/multiplexer with complementary 3-state outputs, designed for bus-oriented digital systems. It operates across 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 logic-level translation and data routing applications.

For engineers reviewing the SN74HC251NSR datasheet, SN74HC251NSR pinout, SN74HC251NSR application, or SN74HC251NSR equivalent, this page provides verified functional modes, validated switching characteristics, confirmed package dimensions, and real-world use cases for bus arbitration, signal routing, and logic-level multiplexing in industrial control and embedded interface design.

Technical Context

The SN74HC251NSR implements full binary decoding to select one of eight data inputs (D0–D7) using three address lines (A, B, C), with strobe-controlled enable (OE) governing complementary 3-state outputs (Y and W). Its dual-output architecture provides true and inverted data simultaneously, enabling direct interfacing with bidirectional system buses.

It features high-current 3-state outputs capable of driving up to 15 LSTTL loads, low input current (≤1 μA max), and low quiescent power consumption (ICC ≤ 80 μA at VCC = 6 V). The device complies with standard HC logic thresholds and supports operation from −40°C to +85°C.

Key Specifications

Pinout & Package

SOP (NS) package, 16-pin, body size 6.20 mm × 5.30 mm, 1.27 mm pitch, 2.00 mm max height, RoHS-compliant, tape-and-reel (2000 pcs/reel), MSL Level-1.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HC251NSR, SN74HC151DR offers marginally lower thermal performance in high-density layouts, while CD74HC251M96 provides identical functionality with no design impact-making it a drop-in logistics alternative rather than a technical substitute.

Availability

SN74HC251NSR is available at Aetrix Electronics and suitable for industrial PLC I/O multiplexing, embedded microcontroller bus expansion, digital audio signal routing, and automated test equipment requiring stable component supply and long-term manufacturability.

Supply support for SN74HC251NSR 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 solutions with over 90 years of innovation in industrial, automotive, and communications markets.

The SN74HC251NSR belongs to TI's 74HC logic family, engineered for high-speed, low-power CMOS operation in bus-oriented digital systems requiring reliable 3-state control and wide supply voltage tolerance.

FAQ

What is the maximum operating frequency supported by SN74HC251NSR?

The SN74HC251NSR does not specify a maximum clock frequency in its datasheet because it is a combinational logic device-not clocked. Its speed is defined by propagation delay: typical tpd = 9 ns at VCC = 4.5 V and CL = 50 pF. This corresponds to a practical data switching limit of ~110 MHz under ideal conditions, though system-level timing margins and load capacitance will determine actual usable rate. SN74HC251NSR performance remains stable across its full 2–6 V supply range.

Does SN74HC251NSR support hot-swap or live-insertion?

SN74HC251NSR is not rated for hot-swap operation. Its absolute maximum ratings do not include powered insertion stress, and the absence of bus-hold or Ioff protection means unpowered VCC or floating inputs during insertion can cause latch-up or excessive current draw. For hot-swap applications, TI recommends dedicated hot-swap controllers or logic families with Ioff specification (e.g., SN74LVC series). SN74HC251NSR must be powered and stabilized before applying input signals.

Can SN74HC251NSR drive a 50-pF transmission line directly?

Yes - SN74HC251NSR can drive a 50-pF capacitive load directly. Its specified switching characteristics (tpd, tt, ten, tdis) are tested at CL = 50 pF, confirming robust performance under that condition. At VCC = 4.5 V, it achieves typical tpd = 41 ns and rise/fall times ≤19 ns. For longer traces or higher-frequency edge rates, series termination near the driver output is recommended to suppress reflections. SN74HC251NSR's ±6 mA drive strength ensures adequate slew rate for such loads.

How does the OE pin behavior affect bus contention in multi-device systems?

The OE pin on SN74HC251NSR is active-low and controls both Y and W outputs simultaneously. When OE is HIGH, both outputs enter high-impedance (Hi-Z) state, electrically disconnecting the device from the bus - eliminating contention with other drivers. When OE is LOW, only the selected output (Y or W) drives the bus; the complementary output mirrors it. This synchronous 3-state control ensures clean bus arbitration in shared-data-path architectures. SN74HC251NSR's guaranteed high-impedance leakage (IOZ ≤ ±5 μA) further prevents unintended loading.

Is SN74HC251NSR compatible with 3.3 V-only systems?

Yes - SN74HC251NSR operates reliably at VCC = 3.3 V. Its recommended operating conditions include 2 V to 6 V, and its input thresholds scale proportionally: VIH(min) = 2.0 V and VIL(max) = 1.0 V at VCC = 3.3 V. Output VOH(min) = 3.15 V and VOL(max) = 0.26 V meet 3.3 V LVTTL requirements. All timing parameters (tpd, ten, etc.) are characterized down to 2 V, ensuring consistent behavior. SN74HC251NSR maintains full functionality without level-shifting in 3.3 V logic domains.