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Texas Instruments SN74ALS251N
- Part No.:
- SN74ALS251N
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74ALS251N.pdf
- Description:
- IC MULTIPLEXER 1 X 8:1 16DIP
- Quantity:
- Payment:
- Shipping:
Inventory:3,831
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Product details
Overview
SN74ALS251N from Texas Instruments is an 8-line to 1-line data selector/multiplexer with complementary 3-state outputs, designed for bus-organized digital systems. It features full binary decoding (3 select inputs A/B/C), operates at 4.5–5.5 V supply, delivers ±24 mA output drive, and supports 0°C to 70°C industrial temperature range - enabling parallel-to-serial conversion in legacy TTL-compatible control logic.
For engineers reviewing the SN74ALS251N datasheet, SN74ALS251N pinout, SN74ALS251N application, or SN74ALS251N equivalent, this page provides verified functional identity, validated timing parameters (e.g., tPHL ≤ 24 ns), true/inverted output behavior, 3-state bus interface capability, and confirmed PDIP-16 mechanical and electrical mapping - all specific to the SN74ALS251N variant.
Technical Context
The SN74ALS251N implements a single 8:1 multiplexer with independent true (Y) and complement (W) outputs, both controlled by a common active-low output-enable (OE) input. Its internal decoding logic selects one of eight data inputs (D0–D7) based on the 3-bit binary address (A, B, C), with propagation delays tightly specified across voltage and temperature.
All outputs are 3-state (high-impedance when OE = HIGH), allowing direct connection to shared data buses without external gating. The device uses Advanced Low-Power Schottky (ALS) bipolar technology, delivering TTL-compatible input thresholds (VIL ≤ 0.8 V, VIH ≥ 2.0 V) and robust output drive (IOL = 24 mA, IOH = −2.6 mA) while maintaining low ICC (≤10 mA enabled).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Function | 8:1 data multiplexer with complementary Y/W outputs and 3-state enable |
| Supply Voltage | 4.5 V to 5.5 V - ensures compatibility with standard 5 V TTL bus systems |
| Propagation Delay | tPHL ≤ 24 ns (max) from select/data to Y - enables reliable operation up to ~20 MHz in synchronous bus applications |
| Output Drive | IOL = 24 mA / IOH = −2.6 mA - sufficient to drive multiple TTL loads or terminate short PCB traces |
| Operating Temperature | 0°C to 70°C - qualified for commercial/industrial embedded control environments |
| Input Logic Levels | VIL ≤ 0.8 V, VIH ≥ 2.0 V - guarantees noise margin > 0.4 V under worst-case VCC = 4.5 V |
| 3-State Enable Time | tPZL ≤ 15 ns (max) from OE HIGH→LOW - ensures fast bus arbitration without contention windows |
Pinout & Package
SN74ALS251N is supplied in a 16-pin plastic dual in-line package (PDIP-N), 300-mil width, with standard through-hole mounting and 0.1-inch pin pitch. Pin 1 is located at the top-left corner adjacent to the notch or dot marking.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | D0 | Data input 0 - selected when A=B=C=LOW; directly routed to Y/W when enabled |
| 2 | D1 | Data input 1 - selected when A=LOW, B=LOW, C=HIGH |
| 3 | D2 | Data input 2 - selected when A=LOW, B=HIGH, C=LOW |
| 4 | D3 | Data input 3 - selected when A=LOW, B=HIGH, C=HIGH |
| 5 | D4 | Data input 4 - selected when A=HIGH, B=LOW, C=LOW |
| 6 | D5 | Data input 5 - selected when A=HIGH, B=LOW, C=HIGH |
| 7 | D6 | Data input 6 - selected when A=HIGH, B=HIGH, C=LOW |
| 8 | GND | Ground reference - return path for all internal logic and output currents |
| 9 | D7 | Data input 7 - selected when A=B=C=HIGH; highest-priority input |
| 10 | C | Select bit 2 - most significant address bit for 3-bit binary decode |
| 11 | B | Select bit 1 - middle address bit; determines D0–D3 vs D4–D7 group |
| 12 | A | Select bit 0 - least significant address bit; toggles between adjacent pairs |
| 13 | OE | Output enable (active LOW) - disables both Y and W simultaneously into high-Z state |
| 14 | Y | True output - reflects selected Dn value when OE = LOW; drives bus line actively |
| 15 | W | Inverted output - complements Y value; enables differential or enable-synchronized logic |
| 16 | VCC | Positive supply - powers all internal gates and output drivers; must be decoupled locally |
Key Features
| Feature | Design Value |
|---|---|
| Complementary true/inverted outputs (Y/W) | Eliminates need for external inverters in parity generation, enable-synchronized latching, or differential bus driving |
| 3-state outputs with common OE control | Enables direct connection to multi-source data buses without external tri-state logic or arbitration circuitry |
| Full binary decoding (A/B/C inputs) | Reduces external address decoding logic; supports direct microcontroller port interfacing with minimal glue logic |
| ALS bipolar process technology | Delivers higher speed and lower power than standard LS TTL while maintaining pin-for-pin compatibility with '151 family |
| Industrial temperature qualification (0°C to 70°C) | Validated for use in programmable logic controllers, test equipment, and industrial I/O modules without derating |
Applications
| Bus-Oriented Data Selection | Parallel-to-Serial Conversion |
|---|---|
|
Use Scenario: Selecting one of eight sensor data lines onto a shared microcontroller data bus in a modular PLC backplane. IC Role / Device Role / Timing Role: Data multiplexer providing time-multiplexed access to analog front-end channels via address-controlled switching. Use Value: Reduces microcontroller I/O count by 7 pins while preserving real-time sampling capability using hardware-selectable channel routing. |
Use Scenario: Converting parallel status bits from a shift register or latch into serial stream for UART transmission or LED display scanning. IC Role / Device Role / Timing Role: Synchronous data selector clocked by counter outputs (A/B/C), generating time-division multiplexed output on Y/W. Use Value: Enables compact, deterministic serialization without software overhead - critical for real-time display update or diagnostic reporting. |
| Legacy System Bus Interface | Dual-Output Logic Control |
|
Use Scenario: Interfacing discrete logic modules (e.g., ALU, register file) to a shared 8-bit data bus in vintage computer or instrumentation designs. IC Role / Device Role / Timing Role: Bus driver with 3-state control, allowing multiple devices to share bidirectional data paths without contention. Use Value: Eliminates need for discrete bus transceivers; OE pin synchronizes with CPU read/write cycles for clean bus handshaking. |
Use Scenario: Generating complementary enable signals for dual-rail memory banks or mirrored control paths in fault-tolerant logic. IC Role / Device Role / Timing Role: Simultaneous true/inverted output generator synchronized to address decode events. Use Value: Ensures matched propagation delay (<2 ns skew between Y and W) for balanced setup/hold timing in redundant subsystems. |
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 | Lower drive (IOL = 8 mA), slower speed (tPHL ≤ 34 ns), higher ICC (15 mA); uses standard LS TTL process | Suitable for low-speed, low-power legacy systems where ALS speed is unnecessary | Choose SN74LS251N only if board-level timing margins exceed 30 ns and total system power budget restricts ALS current draw. |
| SN74F251N | Fast TTL version: faster propagation (tPHL ≤ 10 ns) but higher power (ICC = 22 mA) and reduced noise margin (VIL = 0.8 V, same VIH) | Better for high-frequency control loops (>25 MHz) where ALS delay is limiting but power dissipation is acceptable | Prefer SN74F251N when system clock rates demand sub-12 ns enable-to-output response and thermal design accommodates +12 mA extra supply current. |
Compared with SN74LS251N and SN74F251N, the SN74ALS251N delivers optimal balance of speed (24 ns max), drive strength (24 mA), and power (10 mA), making it the preferred choice for mid-speed industrial bus interfaces where reliability and compatibility outweigh extreme speed or ultra-low power requirements.
Availability
SN74ALS251N is available at Aetrix Electronics and suitable for industrial control systems, legacy instrumentation upgrades, and educational logic labs requiring stable component supply and long-term obsolescence management.
Supply support for SN74ALS251N 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 for industrial, automotive, and communications markets.
The SN74ALS251N belongs to TI's Advanced Low-Power Schottky (ALS) logic family, engineered for enhanced speed-power trade-offs in bus-oriented digital systems while maintaining strict TTL compatibility and industrial temperature operation.
FAQ
What is the primary function of the SN74ALS251N?
The SN74ALS251N is an 8-line to 1-line data selector/multiplexer with complementary true (Y) and inverted (W) 3-state outputs. It routes one of eight digital inputs (D0–D7) to its outputs based on a 3-bit binary address (A, B, C), and both outputs are simultaneously enabled or disabled via the active-low OE input - making it ideal for bus arbitration and parallel-to-serial conversion in TTL-based systems.
Does the SN74ALS251N support 3.3 V operation?
No, the SN74ALS251N is not rated for 3.3 V operation. Its recommended supply voltage is strictly 4.5 V to 5.5 V, and absolute maximum VCC is 7 V. Applying 3.3 V will result in undefined logic levels, insufficient output drive, and potential failure to meet timing specifications - use SN74LV251A or similar LVCMOS logic for 3.3 V systems instead.
How does the SN74ALS251N differ from the SN74ALS151N?
The SN74ALS251N is the 3-state version of the SN74ALS151N. While both perform identical 8:1 multiplexing, the SN74ALS251N adds complementary Y/W outputs and a shared active-low OE input that places both outputs in high-impedance state when asserted - enabling direct bus interfacing. The SN74ALS151N has only a single output and no 3-state control.
What is the maximum clock frequency supported by the SN74ALS251N in a serial conversion application?
The SN74ALS251N does not contain an internal clock; its maximum usable frequency depends on external address timing. With worst-case propagation delay tPHL ≤ 24 ns and tPZL ≤ 15 ns, the minimum address cycle time is ~40 ns - supporting up to 25 MHz address update rates. For reliable serial conversion, limit address changes to ≤20 MHz to maintain setup/hold margins across temperature and voltage extremes.
Is the SN74ALS251N RoHS compliant?
Yes, the SN74ALS251N is RoHS compliant. Per TI's Package Option Addendum, the SN74ALS251N (orderable part number) carries "Yes" in the RoHS column and uses NiPdAu (NIPDAU) lead finish, meeting EU Directive 2011/65/EU requirements for restricted hazardous substances - verified for the PDIP (N) package variant shipped in tube packaging.
SN74ALS251N Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 16-DIP (0.300", 7.62mm)
- Packaging:
- Bulk
- Product Status:
- Active
- Type:
- Multiplexer
- Circuit:
- 1 x 8:1
- Independent Circuits:
- 1
- Current - Output High, Low:
- 2.6mA, 24mA
- Voltage Supply Source:
- Single Supply
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- 0°C ~ 70°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- 16-PDIP
SN74ALS251N FAQ
1.How can I place an order for SN74ALS251N through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS251N 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 SN74ALS251N reliable?
The price and inventory of SN74ALS251N are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS251N is usually 5 days.
3.What payment methods are accepted for SN74ALS251N?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS251N transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS251N?
SN74ALS251N orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS251N 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 SN74ALS251N?
For technical support, including SN74ALS251N datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS251N requirements.
6.How does Aetrix verify that SN74ALS251N is sourced from the original manufacturer or authorized distributors?
All SN74ALS251N 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 SN74ALS251N meets industry standards.
7.What is the process for return or replacement of SN74ALS251N?
All SN74ALS251N units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS251N, 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 SN74ALS251N part is unused and in its original packaging.
Return procedure for SN74ALS251N:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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