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Home > Products > Integrated Circuits (ICs) > Logic > Signal Switches, Multiplexers, Decoders

Texas Instruments SN74LS251DR

Name: SN74LS251DR
Brand: Texas Instruments
SKU: SN74LS251DR
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: SN74LS251DR

Manufacturer:: Texas Instruments

Category:: Signal Switches, Multiplexers, Decoders

Package:: 16-SOIC (0.154", 3.90mm Width)

Datasheet:: SN74LS251DR.pdf

Description:: IC MULTIPLEXER 1 X 8:1 16SOIC

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Product details

Overview

SN74LS251DR from Texas Instruments is a dual 4-line-to-1-line data selector/multiplexer with three-state outputs, implemented in TTL logic, operating over 0°C to 70°C, featuring typical propagation delay of 22 ns at V_CC = 5 V and I_OL = 8 mA, used for digital signal routing in bus-oriented systems such as address/data multiplexing in microprocessor peripherals.

For engineers reviewing the SN74LS251DR datasheet, SN74LS251DR pinout, SN74LS251DR application, or SN74LS251DR equivalent, this device supports logic-level selection of one of eight inputs (via 3-bit address), enables bidirectional bus control via active-low output enable, and delivers TTL-compatible drive strength for legacy industrial control and test equipment interfacing.

Technical Context

The SN74LS251DR implements a single 8:1 multiplexer function with complementary address decoding logic and an active-low 3-state output enable (OE̅), allowing direct connection to shared data buses without external gating. Its internal architecture uses standard LS-TTL bipolar transistor stages with Schottky-clamped inputs and outputs.

It accepts three binary select lines (A, B, C) to route one of eight data inputs (I₀–I₇) to the Y output, while the complementary Y̅ output provides inverted logic level; both outputs are simultaneously enabled or disabled by OE̅, supporting time-multiplexed signal arbitration in synchronous digital subsystems.

Key Specifications

Parameter	Value and Actual Design Meaning
Logic Family	74LS (Low-power Schottky TTL), ensuring compatibility with legacy 5-V TTL systems and predictable noise margins.
Function	8-input, 1-output data selector/multiplexer with complementary Y/Y̅ outputs and 3-state output control.
Propagation Delay	22 ns max (t_PLH/t_PHL at V_CC = 5 V, R_L = 400 Ω, C_L = 15 pF), enabling reliable operation in 20-MHz-class synchronous logic.
Output Drive	I_OH = –0.4 mA / I_OL = 8 mA (min), sufficient to drive 10 standard TTL loads or interface directly with 74LS/74ALS inputs.
Supply Voltage	V_CC = 4.75 V to 5.25 V, requiring stable 5-V rail with ±5% tolerance for guaranteed switching performance.
Operating Temperature	0°C to +70°C ambient, validated for commercial-grade embedded controllers, instrumentation, and lab equipment.
Package	SOIC-16 (D package), 7.5-mm body width, 1.27-mm lead pitch, RoHS-compliant NiPdAu finish, MSL Level-1.

Pinout & Package

SN74LS251DR is housed in a 16-pin SOIC (Small Outline Integrated Circuit) package per TI drawing D, with 1.27-mm lead pitch, 7.5-mm body width, and 2.00-mm maximum height. Pin 1 is located at the top-left corner with notch or beveled edge marking.

Pin/Terminal	Circuit Role	Design Meaning
1 (Y̅)	Inverted multiplexer output	Active-high complement of selected input; enables differential bus signaling or logic inversion without external gate.
2 (I₀)	Data input 0	Low-order input channel selected when A=0, B=0, C=0; TTL-compatible voltage thresholds (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V).
3 (I₁)	Data input 1	Second input channel selected when A=1, B=0, C=0; shares same DC loading and timing characteristics as all I₀–I₇.
4 (I₂)	Data input 2	Third input channel selected when A=0, B=1, C=0; internally terminated with standard LS-TTL input structure.
5 (I₃)	Data input 3	Fourth input channel selected when A=1, B=1, C=0; no internal pull-up/pull-down; requires external bias if floating.
6 (I₄)	Data input 4	Fifth input channel selected when A=0, B=0, C=1; identical AC/DC specs to other data inputs.
7 (I₅)	Data input 5	Sixth input channel selected when A=1, B=0, C=1; supports DC-coupled or AC-coupled signal sources within TTL voltage range.
8 (GND)	Ground reference	Primary return path for all internal current sinks; must be low-impedance and adjacent to V_CC decoupling.
9 (I₆)	Data input 6	Seventh input channel selected when A=0, B=1, C=1; electrically identical to I₀–I₅ and I₇.
10 (I₇)	Data input 7	Highest-order input channel selected when A=1, B=1, C=1; full 8-channel selection coverage with no gaps.
11 (C)	Address bit C (MSB)	Most-significant select line; determines high/low group of four inputs (I₀–I₃ vs. I₄–I₇).
12 (B)	Address bit B	Mid-significance select line; partitions each group of four into two pairs (e.g., I₀/I₁, I₂/I₃).
13 (A)	Address bit A (LSB)	Least-significant select line; selects individual input within each pair (e.g., I₀ or I₁).
14 (OE̅)	Output enable (active low)	Disables both Y and Y̅ outputs to high-impedance state; required for bus sharing; asserted low to enable outputs.
15 (Y)	Multiplexer output	Active-high selected data output; driven to valid TTL logic levels only when OE̅ = LOW.
16 (V_CC)	Positive supply	+5 V power input; requires local 0.1-µF ceramic decoupling capacitor placed within 5 mm of pin.

Key Features

Feature	Design Value
Three-state outputs	Enables direct connection to shared data buses without contention; OE̅ controls simultaneous disable of Y and Y̅.
Complementary outputs (Y/Y̅)	Provides both true and inverted logic levels from same selection event, eliminating need for external inverters in differential interfaces.
Standard TTL-compatible inputs	Accepts 0.8 V/2.0 V logic thresholds and drives 10 standard TTL loads, ensuring interoperability with 74xx, 74LSxx, and 74ALSxx families.
Low-power Schottky process	Reduces dynamic power consumption versus standard TTL while maintaining speed-typical I_CC = 24 mA at 5 MHz toggle rate.
Single 8:1 multiplexer function	Integrates full address decoding, input gating, and output buffering in one IC, reducing board space versus discrete gate solutions.

Applications

Microprocessor Address/Data Bus Multiplexing	Digital Test Equipment Signal Routing
Use Scenario: Selecting between multiple peripheral address latches or data buffers in an 8-bit microcontroller system with limited address lines. IC Role / Device Role / Timing Role: Acts as a programmable signal router under CPU control, using A/B/C lines derived from port pins to steer memory-mapped I/O data. Use Value: Reduces external logic count by consolidating eight discrete paths into one IC, lowering PCB layer count and improving timing predictability.	Use Scenario: Switching calibration reference signals or sensor inputs into a shared ADC channel in automated test fixtures. IC Role / Device Role / Timing Role: Provides deterministic, glitch-free analog multiplexing control when paired with slow-sampling ADCs and static address generation. Use Value: Eliminates mechanical relay wear and contact resistance drift, delivering repeatable 12-bit measurement accuracy across 8 channels.
Legacy Industrial Control Panel Logic	Education & Lab Training Boards
Use Scenario: Implementing mode-select logic in PLC I/O modules where front-panel DIP switches configure operational behavior. IC Role / Device Role / Timing Role: Interprets switch-encoded configuration bits to route status flags, error codes, or diagnostic outputs to indicator LEDs or serial UART. Use Value: Enables field-reconfigurable functionality without firmware update; supports hot-swap replacement due to robust TTL drive.	Use Scenario: Demonstrating combinational logic design principles in undergraduate digital electronics labs using breadboard-based prototyping. IC Role / Device Role / Timing Role: Serves as a hands-on example of data selection, truth table verification, and timing analysis with oscilloscope probes on Y/Y̅ outputs. Use Value: Offers visible, measurable propagation delay and clear pin-level interaction-ideal for teaching multiplexer fundamentals and bus arbitration concepts.

Microprocessor Address/Data Bus Multiplexing

Digital Test Equipment Signal Routing

Use Scenario: Selecting between multiple peripheral address latches or data buffers in an 8-bit microcontroller system with limited address lines.

IC Role / Device Role / Timing Role: Acts as a programmable signal router under CPU control, using A/B/C lines derived from port pins to steer memory-mapped I/O data.

Use Value: Reduces external logic count by consolidating eight discrete paths into one IC, lowering PCB layer count and improving timing predictability.

Use Scenario: Switching calibration reference signals or sensor inputs into a shared ADC channel in automated test fixtures.

IC Role / Device Role / Timing Role: Provides deterministic, glitch-free analog multiplexing control when paired with slow-sampling ADCs and static address generation.

Use Value: Eliminates mechanical relay wear and contact resistance drift, delivering repeatable 12-bit measurement accuracy across 8 channels.

Legacy Industrial Control Panel Logic

Education & Lab Training Boards

Use Scenario: Implementing mode-select logic in PLC I/O modules where front-panel DIP switches configure operational behavior.

IC Role / Device Role / Timing Role: Interprets switch-encoded configuration bits to route status flags, error codes, or diagnostic outputs to indicator LEDs or serial UART.

Use Value: Enables field-reconfigurable functionality without firmware update; supports hot-swap replacement due to robust TTL drive.

Use Scenario: Demonstrating combinational logic design principles in undergraduate digital electronics labs using breadboard-based prototyping.

IC Role / Device Role / Timing Role: Serves as a hands-on example of data selection, truth table verification, and timing analysis with oscilloscope probes on Y/Y̅ outputs.

Use Value: Offers visible, measurable propagation delay and clear pin-level interaction-ideal for teaching multiplexer fundamentals and bus arbitration concepts.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
SN74LS151N	Identical logic function, pinout, and electrical specs; differs only in PDIP-16 packaging (vs. SOIC-16 for SN74LS251DR).	Preferred for through-hole prototyping or legacy repair where SOIC rework is impractical.	Select SN74LS151N when manual soldering or socket-based testing is required; SN74LS251DR is optimal for surface-mount production.
SN74LS251NSR	Same function and SOIC-16 footprint but uses SOP-16 package (TI drawing NS); slightly wider body (7.5 mm vs. 3.9 mm) and different tape-and-reel dimensions.	Used in legacy board designs specifying NS package; not mechanically interchangeable with D-package SN74LS251DR.	Choose SN74LS251NSR only if existing PCB land pattern matches SOP-16 NS outline; otherwise use SN74LS251DR for standard SOIC-16 layouts.

Compared with SN74LS151N and SN74LS251NSR, the SN74LS251DR offers RoHS-compliant NiPdAu plating, MSL Level-1 reflow compatibility, and optimized tape-and-reel packaging for automated SMT assembly-making it the preferred choice for new commercial-grade surface-mount designs requiring long-term supply stability.

Availability

SN74LS251DR is available at Aetrix Electronics and suitable for microprocessor peripheral interfacing, digital test equipment signal routing, legacy industrial control panel logic, and educational lab training boards requiring stable component supply and long-lifecycle support.

Supply support for SN74LS251DR 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 U.S.-based semiconductor company founded in 1930, specializing in analog, embedded processing, and logic products with broad industrial, automotive, and consumer reach.

The SN74LS251DR belongs to TI's legacy 74LS logic family, designed specifically for backward-compatible upgrades of 74-series TTL systems requiring low power, moderate speed, and robust noise immunity in commercial environments.

FAQ

What is the primary logic function of the SN74LS251DR?

The SN74LS251DR is an 8-line-to-1-line data selector/multiplexer with complementary Y and Y̅ outputs and active-low 3-state output enable (OE̅). It routes one of eight digital inputs (I₀–I₇) to the Y output based on the binary value of address lines A, B, and C. The SN74LS251DR also provides the inverted signal at Y̅ and disables both outputs when OE̅ is high, making it suitable for bus-oriented architectures.

Does the SN74LS251DR support 3.3-V logic systems?

No, the SN74LS251DR is a 5-V-only TTL device with V_CC specified from 4.75 V to 5.25 V. Its input thresholds (V_IL ≤ 0.8 V, V_IH ≥ 2.0 V) and output drive levels are optimized for 5-V operation and are not compatible with 3.3-V CMOS or LVTTL logic without level-shifting circuitry. Using the SN74LS251DR in a 3.3-V system risks unreliable switching or excessive current draw.

What is the maximum clock or data toggle rate supported by the SN74LS251DR?

The SN74LS251DR does not operate on a clock signal-it is purely combinational logic. Its usable data rate is governed by propagation delay (22 ns max) and setup/hold timing of address inputs relative to data stability. For reliable operation, address lines should be stable ≥20 ns before and after data transitions, supporting effective multiplexing rates up to approximately 20 MHz in well-designed synchronous systems using the SN74LS251DR.

Can the SN74LS251DR be used as a demultiplexer?

No, the SN74LS251DR is not configured for demultiplexing. It has a single-directional data path: eight inputs feeding one output (Y) and its complement (Y̅). Demultiplexing requires one input routed to multiple outputs-a function provided by devices like the SN74LS138 or SN74LS139, not the SN74LS251DR. Attempting to reverse-use the SN74LS251DR as a demux will not yield correct logic behavior.

Is there a drop-in replacement for the SN74LS251DR with improved power efficiency?

No pin-compatible, functionally identical low-power replacement exists for the SN74LS251DR. While CMOS alternatives like the CD74HC251 offer lower static power, they differ in voltage range (2–6 V), input thresholds, drive strength, and timing-requiring redesign of interface circuitry. The SN74LS251DR remains the standard for direct 74LS TTL replacement; any upgrade must account for these electrical and timing mismatches.

SN74LS251DR Specifications

Product attributes: Attribute value

Manufacturer:: Texas Instruments

Series:: 74LS

Package/Case:: 16-SOIC (0.154", 3.90mm Width)

Packaging:: Tape & Reel (TR)

Product Status:: Active

Type:: Multiplexer

Circuit:: 1 x 8:1

Independent Circuits:: 1

Current - Output High, Low:: 2.6mA, 8mA

Voltage Supply Source:: Single Supply

Voltage - Supply:: 4.75V ~ 5.25V

Operating Temperature:: 0°C ~ 70°C

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: 16-SOIC

SN74LS251DR FAQ

1.How can I place an order for SN74LS251DR through Aetrix?

Please submit a Request for Quotation (RFQ) for SN74LS251DR on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for SN74LS251DR reliable?

The price and inventory of SN74LS251DR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS251DR is usually 5 days.

3.What payment methods are accepted for SN74LS251DR?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS251DR transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for SN74LS251DR?

SN74LS251DR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your SN74LS251DR order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for SN74LS251DR?

For technical support, including SN74LS251DR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS251DR requirements.

6.How does Aetrix verify that SN74LS251DR is sourced from the original manufacturer or authorized distributors?

All SN74LS251DR products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that SN74LS251DR meets industry standards.

7.What is the process for return or replacement of SN74LS251DR?

All SN74LS251DR units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS251DR, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The SN74LS251DR part is unused and in its original packaging.

Return procedure for SN74LS251DR:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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