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

Texas Instruments SN74S251N

Name: SN74S251N
Brand: Texas Instruments
SKU: SN74S251N
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: SN74S251N

Manufacturer:: Texas Instruments

Category:: Signal Switches, Multiplexers, Decoders

Package:: -

Datasheet:: SN74S251N.pdf

Description:: MUX, 8 LINE INPUT

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Product details

Overview

SN74S251N from Texas Instruments is a high-speed TTL 8-line to 1-line data selector/multiplexer with three-state outputs, operating at V_CC = 4.75–5.25 V, propagation delay t_pd = 10 ns (max), and fan-out of 10 LSTTL loads, used in digital logic routing, address decoding, and bus multiplexing in industrial control and instrumentation systems.

For engineers reviewing the SN74S251N datasheet, SN74S251N pinout, SN74S251N application, or SN74S251N equivalent, key selection considerations include its 16-pin PDIP package, active-low enable (G̅), dual complementary outputs (Y and Y̅), and compatibility with standard TTL logic families in legacy system upgrades and repair.

Technical Context

The SN74S251N implements a full 3-bit binary-select 8:1 multiplexer architecture with independent strobe control via G̅, supporting both true (Y) and complemented (Y̅) output paths simultaneously. Its Schottky-clamped transistor design enables faster switching than standard 74LS devices while maintaining TTL voltage thresholds.

It features three-state output drivers with common enable, allowing direct connection to shared data buses without external gating. Input clamping diodes and internal current-limiting resistors provide robust noise immunity and DC drive capability across its full operating temperature range (0°C to +70°C).

Key Specifications

Parameter	Value and Actual Design Meaning
V_CC Supply	4.75 V to 5.25 V - Ensures stable operation within standard TTL rail tolerance, compatible with legacy 5 V logic systems.
Propagation Delay	10 ns (max) - Enables reliable operation in high-speed digital systems up to ~50 MHz clock domains for combinatorial routing.
Output Drive	I_OH/I_OL = –1.6 mA / 20 mA - Sufficient to directly drive 10 LSTTL inputs or small capacitive loads (<30 pF) without buffering.
Enable Logic	Active-low G̅ input - Allows synchronous bus arbitration and hierarchical multiplexing when cascaded with other select-enabled devices.
Operating Temperature	0°C to +70°C - Qualified for commercial-grade applications including test equipment, PLC I/O modules, and lab instrumentation.
Package Type	16-pin PDIP (N) - Through-hole mounting compatible with prototyping, repair, and legacy PCB assembly workflows.

Pinout & Package

SN74S251N is housed in a 16-pin plastic dual in-line package (PDIP), 0.300-inch body width, with 0.100-inch lead pitch and standard DIP footprint (JEDEC MS-001). Pin 1 is marked by a notch or dot at the top-left corner.

Pin/Terminal	Circuit Role	Design Meaning
1 (G̅)	Output Enable (active low)	Disables both Y and Y̅ outputs to high-impedance state; required for bus sharing and multi-device arbitration.
2–4 (C, B, A)	Binary Select Inputs	3-bit address determining which of eight data inputs (D0–D7) routes to Y/Y̅; LSB = A, MSB = C.
5–12 (D0–D7)	Data Inputs	Eight parallel digital inputs; each independently sampled based on CBA code; no internal latching.
13 (Y̅)	Inverted Output	Complementary active-high output of selected input; supports differential signaling or NAND/NOR logic expansion.
14 (V_CC)	Positive Supply	5 V power rail; requires local 0.1 µF ceramic bypass capacitor near pin for noise suppression.
15 (Y)	True Output	Non-inverted output of selected input; usable as primary routed signal path in combinational logic blocks.
16 (GND)	Ground Reference	Signal and power return; must be connected to low-impedance ground plane to minimize switching noise coupling.

Key Features

Feature	Design Value
High-Speed Schottky TTL	10 ns max propagation delay enables use in timing-critical address/data routing where LS-series delays are insufficient.
Dual Complementary Outputs	Simultaneous Y and Y̅ outputs eliminate need for external inverters in applications requiring both polarities (e.g., ALU control).
Three-State Output Control	G̅-enabled high-impedance mode allows direct connection to shared data buses without contention or external tri-state buffers.
Standard TTL Compatibility	Input thresholds and output voltages fully align with 74TTL/74S logic families, enabling drop-in replacement in existing designs.
Robust Input Clamping	Integrated input diodes protect against transient overvoltage (±0.5 V beyond rails), improving reliability in noisy industrial environments.

Applications

Address Decoding	Bus Multiplexing
Use Scenario: Selecting one of eight memory-mapped peripheral registers in a microprocessor-based controller. IC Role / Device Role / Timing Role: 8:1 data selector translating 3-bit address lines into single-register access path with sub-12 ns latency. Use Value: Eliminates discrete gate-based decoder trees, reducing board area and propagation skew across register selection paths.	Use Scenario: Routing sensor data from eight analog front-end channels onto a shared ADC interface bus. IC Role / Device Role / Timing Role: High-speed analog switch controller synchronizing channel selection with sample-hold timing signals. Use Value: Maintains signal integrity through low-capacitance, matched-path routing-critical for <12-bit measurement accuracy.
Logic Function Generation	Test Equipment Signal Routing
Use Scenario: Implementing custom combinational logic (e.g., parity generator, custom ALU opcode decoder) using hardwired D0–D7 inputs. IC Role / Device Role / Timing Role: Programmable logic element configured via fixed D-input wiring and dynamic CBA selection. Use Value: Provides field-configurable logic without FPGA overhead-ideal for low-volume, cost-sensitive embedded controllers.	Use Scenario: Switching calibration reference signals between multiple instrument channels in automated test systems. IC Role / Device Role / Timing Role: Precision signal router with guaranteed monotonic switching and minimal glitch energy during transitions. Use Value: Reduces calibration drift by avoiding mechanical relays; supports >100 kcycles reliability in production test fixtures.

Address Decoding

Bus Multiplexing

Use Scenario: Selecting one of eight memory-mapped peripheral registers in a microprocessor-based controller.

IC Role / Device Role / Timing Role: 8:1 data selector translating 3-bit address lines into single-register access path with sub-12 ns latency.

Use Value: Eliminates discrete gate-based decoder trees, reducing board area and propagation skew across register selection paths.

Use Scenario: Routing sensor data from eight analog front-end channels onto a shared ADC interface bus.

IC Role / Device Role / Timing Role: High-speed analog switch controller synchronizing channel selection with sample-hold timing signals.

Use Value: Maintains signal integrity through low-capacitance, matched-path routing-critical for <12-bit measurement accuracy.

Logic Function Generation

Test Equipment Signal Routing

Use Scenario: Implementing custom combinational logic (e.g., parity generator, custom ALU opcode decoder) using hardwired D0–D7 inputs.

IC Role / Device Role / Timing Role: Programmable logic element configured via fixed D-input wiring and dynamic CBA selection.

Use Value: Provides field-configurable logic without FPGA overhead-ideal for low-volume, cost-sensitive embedded controllers.

Use Scenario: Switching calibration reference signals between multiple instrument channels in automated test systems.

IC Role / Device Role / Timing Role: Precision signal router with guaranteed monotonic switching and minimal glitch energy during transitions.

Use Value: Reduces calibration drift by avoiding mechanical relays; supports >100 kcycles reliability in production test fixtures.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
SN74LS251N	Slower propagation delay (23 ns max); lower drive strength (I_OL = 8 mA); same pinout and function.	Better suited for low-power, non-timing-critical systems where speed margin is not required.	Select SN74LS251N only if system timing budget allows ≥23 ns delay and reduced output loading is acceptable.
SN74F251N	Faster delay (8 ns max); higher power consumption; identical pinout and truth table.	Preferred in high-frequency digital systems where <10 ns routing latency is mandatory.	Choose SN74F251N when maximum speed is critical and thermal/power constraints permit higher IDD.

Compared with SN74LS251N and SN74F251N, the SN74S251N delivers optimal balance of speed (10 ns), drive capability (20 mA sink), and power efficiency-making it the preferred choice for mid-speed industrial control and instrumentation where reliability and timing margin coexist.

Availability

SN74S251N is available at Aetrix Electronics and suitable for industrial control systems, test instrumentation, and legacy system repair requiring stable component supply and long-term obsolescence mitigation.

Supply support for SN74S251N 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 founded in 1930, specializing in analog, embedded processing, and logic solutions with broad industrial, automotive, and aerospace qualification.

The SN74S251N belongs to TI's legacy 74S logic family, engineered for high-speed digital routing in commercial and industrial systems where robustness, pin compatibility, and proven field reliability outweigh ultra-low power requirements.

FAQ

What is the maximum clock frequency supported by SN74S251N in a synchronous multiplexing application?

The SN74S251N is a combinational device with no internal clock; its effective maximum operating frequency depends on propagation delay and system setup/hold timing. With t_pd = 10 ns (max) and typical interconnect delays, SN74S251N reliably supports synchronous selection rates up to 50 MHz in well-designed PCB layouts. For precise timing analysis, engineers must verify total path delay-including driver rise time and load capacitance-in their specific SN74S251N implementation.

Does SN74S251N support hot-swap or live-insertion on a powered backplane?

No, SN74S251N does not support hot-swap operation. Its inputs lack power-on reset, bus-hold, or I²C-style slew-rate control. Applying signals before V_CC stabilization may cause latch-up or undefined output states. Always power the SN74S251N supply before applying input signals or connecting to live buses. This limitation applies to all variants of the SN74S251N.

Can SN74S251N be used as a level shifter between 5 V TTL and 3.3 V logic?

No, SN74S251N is not designed for level shifting. It operates strictly at 5 V (4.75–5.25 V) and its outputs swing to TTL-compatible levels (~3.5 V VOH, ~0.5 V VOL). Driving 3.3 V CMOS inputs directly risks overvoltage stress and excessive input leakage. Use dedicated level translators (e.g., TXB0108) or resistor-divider networks-not SN74S251N-for interfacing with 3.3 V logic domains.

Is there a RoHS-compliant version of SN74S251N currently in production?

Yes, SN74S251N is RoHS-compliant with NiPdAu (NIPDAU) lead finish and meets JEDEC J-STD-020 moisture sensitivity Level-1 rating. The part marking "SN74S251N" appears on RoHS-compliant units, and TI confirms full compliance per EU Directive 2011/65/EU. No exemptions apply; lead content is below 1000 ppm threshold across all homogeneous materials in the SN74S251N package.

How does the three-state output behavior of SN74S251N interact with bus contention in multi-device configurations?

When G̅ is high, both Y and Y̅ enter high-impedance (Hi-Z) state, electrically disconnecting the SN74S251N from the bus. This prevents contention with other three-state drivers (e.g., microprocessor data bus, other multiplexers). Proper bus arbitration requires strict synchronization of G̅ control signals-only one device should have G̅ low at any time. Failure to coordinate G̅ timing across devices may cause short-duration bus conflicts, potentially damaging outputs in sustained contention scenarios involving SN74S251N.

SN74S251N Specifications

Product attributes: Attribute value

Manufacturer:: Texas Instruments

Series:: *

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Packaging:: Bulk

Product Status:: Active

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Current - Output High, Low:: -

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Voltage - Supply:: -

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SN74S251N FAQ

1.How can I place an order for SN74S251N through Aetrix?

Please submit a Request for Quotation (RFQ) for SN74S251N 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 SN74S251N reliable?

The price and inventory of SN74S251N are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74S251N is usually 5 days.

3.What payment methods are accepted for SN74S251N?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74S251N transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for SN74S251N?

SN74S251N orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your SN74S251N 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 SN74S251N?

For technical support, including SN74S251N datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74S251N requirements.

6.How does Aetrix verify that SN74S251N is sourced from the original manufacturer or authorized distributors?

All SN74S251N 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 SN74S251N meets industry standards.

7.What is the process for return or replacement of SN74S251N?

All SN74S251N units undergo pre-shipment inspection (PSI). If there is an issue with SN74S251N, 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 SN74S251N part is unused and in its original packaging.

Return procedure for SN74S251N:

1.Submit a request within 90 days.

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

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