Texas Instruments SN74HC251DBR

Overview

SN74HC251DBR 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 SN74HC251DBR datasheet, SN74HC251DBR pinout, SN74HC251DBR application, or SN74HC251DBR equivalent, this page provides verified functional modes, switching characteristics, thermal metrics, package-specific layout guidance, and real-world use context for system integration and BOM validation.

Technical Context

The SN74HC251DBR implements full binary decoding of three select inputs (A, B, C) to route one of eight data inputs (D0–D7) to complementary outputs Y and W, both controlled by a single active-low output-enable (OE) signal. Its 3-state architecture allows direct connection to shared data buses without external buffering.

It features complementary true/inverted outputs, low input current (≤1 μA), high-current 3-state drivers capable of sinking/sourcing up to 6 mA at 5 V, and guaranteed operation over –40°C to +85°C ambient temperature with supply voltage ranging from 2 V to 6 V.

Key Specifications

Pinout & Package

SN74HC251DBR uses a 16-pin SSOP (Shrink Small Outline Package) with body size 6.20 mm × 5.30 mm and 0.65 mm lead pitch. The package is RoHS-compliant, moisture sensitivity level 1, and rated for reflow up to 260°C.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74HCT251DBR and CD74HC251M96, the SN74HC251DBR provides optimal balance of package miniaturization (SSOP-16), industrial temperature range, and ultra-low quiescent current - making it ideal for space-constrained, battery-aware, or thermally managed embedded systems where precise CMOS-level compatibility is required.

Availability

SN74HC251DBR is available at Aetrix Electronics and suitable for industrial control I/O expansion, microcontroller peripheral multiplexing, digital test equipment signal routing, and legacy system bus interface applications requiring stable component supply and long-term manufacturability.

Supply support for SN74HC251DBR 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 experience delivering high-reliability, industry-standard logic families.

The SN74HC251DBR belongs to TI's 74HC high-speed CMOS logic series, engineered for low-power, wide-supply-operation digital signal routing in industrial, automotive, and communications equipment.

FAQ

What is the maximum operating frequency supported by SN74HC251DBR?

The SN74HC251DBR does not specify a maximum clock or data rate in its datasheet. Its performance is defined by propagation delay (tpd ≤ 60 ns at VCC = 4.5 V, CL = 50 pF) and transition time limits (Δt/Δv ≤ 500 ns at VCC = 4.5 V). For reliable operation, input signal edges must meet these slew-rate requirements, and system timing must budget for worst-case tpd plus setup/hold margins. The SN74HC251DBR is intended for asynchronous data selection, not synchronous clocked operation.

Can SN74HC251DBR operate with a 3.3 V supply?

Yes, SN74HC251DBR is fully specified for operation at 3.3 V. Its recommended operating conditions include VCC = 2 V to 6 V, and electrical characteristics such as VOH ≥ 3.15 V (min) and VOL ≤ 0.33 V (max) are guaranteed at VCC = 4.5 V - well within 3.3 V system margins. At 3.3 V, output drive remains robust (±4 mA typical), and input thresholds scale proportionally, ensuring reliable interfacing with 3.3 V microcontrollers and FPGAs.

How does the OE pin function on SN74HC251DBR?

The OE (Output Enable) pin on SN74HC251DBR is active-low: when OE = L (≤0.8 V), outputs Y and W are enabled and reflect the selected data; when OE = H (≥2.0 V at VCC = 4.5 V), both outputs enter high-impedance (3-state) mode regardless of select or data inputs. This allows multiple SN74HC251DBR devices to share a common bus - only the device with OE asserted drives the line, preventing contention.

Is SN74HC251DBR pin-compatible with SN74HC151?

Yes, SN74HC251DBR is a 3-state version of the 'HC151 and shares identical pinout, functionality, and truth table with SN74HC151DBR. Both devices use the same 16-pin SSOP package (DB), have matching A/B/C/D0–D7/OE/Y/W assignments, and operate across 2–6 V. The key difference is that SN74HC251DBR adds complementary W output and 3-state control - SN74HC151 provides only Y output with open-collector-like behavior.

What is the thermal resistance (RθJA) of SN74HC251DBR in its SSOP package?

The junction-to-ambient thermal resistance (RθJA) for SN74HC251DBR in the SSOP-16 (DB) package is 82°C/W, as specified in Section 5.3 of the TI datasheet. This value assumes standard JEDEC JESD51-2 PCB mounting conditions (single-layer copper, 1 in² pad). For higher-power or compact layouts, thermal performance can be improved using internal copper planes, thermal vias, or reduced ambient temperature - but SN74HC251DBR's max ICC of 80 μA ensures negligible self-heating under normal operation.