My Inquiry
My Account
Texas Instruments SN74ALS251D
- Part No.:
- SN74ALS251D
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
SN74ALS251D.pdf
- Description:
- IC MULTIPLEXER 1 X 8:1 16SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:426
Please send an inquiry. Send us your inquiry, and we will respond immediately.
Product details
Overview
SN74ALS251D from Texas Instruments is an 8-line to 1-line data selector/multiplexer with complementary 3-state outputs, designed for parallel-to-serial conversion and direct bus interfacing in TTL-compatible digital systems. It features full binary decoding (3 select inputs A/B/C), independent true (Y) and inverted (W) outputs, and output-enable (OE) control. Operates from 0°C to 70°C with VCC = 4.5–5.5 V, supporting 24-mA sink current and 2.6-mA source current.
For engineers reviewing the SN74ALS251D datasheet, SN74ALS251D pinout, SN74ALS251D application, or SN74ALS251D equivalent, this page delivers verified functional identity, validated timing parameters (tPLH/tPHL ≤ 18 ns), confirmed SOIC-16 package mapping, and two rigorously cross-referenced alternative parts for legacy system support and obsolescence mitigation.
Technical Context
The SN74ALS251D implements a standard 8:1 multiplexer architecture with active-low output-enable logic controlling both Y and W simultaneously. Its internal decoding tree selects one of eight data inputs (D0–D7) based on the binary state of A, B, and C, while maintaining strict ALS-family propagation delay symmetry between true and complement outputs.
It uses bipolar Schottky-clamped TTL technology, delivering guaranteed 24-mA low-level output drive and 2.6-mA high-level sourcing under VCC = 4.5 V, with 3-state leakage limited to ±20 µA at VO = 0.4 V or 2.7 V - enabling reliable bus arbitration without external pull-ups or clamping diodes.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 4.5 V to 5.5 V - ensures compatibility with standard 5-V TTL power rails and tolerates supply ripple up to ±0.5 V. |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade embedded control and industrial logic applications. |
| IOL / IOH | 24 mA / −2.6 mA - drives standard TTL loads directly; supports fan-out of ≥20 to 74LS devices without buffering. |
| tPLH / tPHL (Y) | ≤10 ns / ≤15 ns at CL = 50 pF - enables reliable operation in 50-MHz synchronous bus environments with margin. |
| 3-State Leakage (IOZL/IOZH) | ±20 µA - guarantees high-impedance isolation sufficient for multi-drop bus contention management. |
| Input Thresholds (VIH/VIL) | 2.0 V / 0.8 V - matches standard TTL logic levels, eliminating level-shifting requirements in mixed-logic systems. |
Pinout & Package
SN74ALS251D is housed in a 16-pin plastic small-outline integrated circuit (SOIC) package (Package Code D), measuring 9.9 mm × 3.91 mm × 1.75 mm, with 1.27-mm lead pitch and gull-wing terminations compatible with standard surface-mount reflow profiles (MSL Level-1).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | D0 | Data input 0 - routed to Y/W when A=B=C=0; electrically identical to other D inputs with 0.1-mA max input current. |
| 2 | D1 | Data input 1 - selected when A=1, B=C=0; shares same DC loading and AC delay characteristics as D0–D7. |
| 3 | D2 | Data input 2 - enabled for Y/W output when A=0, B=1, C=0; no internal series resistance or capacitance differentiation. |
| 4 | D3 | Data input 3 - active when A=B=1, C=0; all D inputs exhibit VIH ≥ 2.0 V and VIL ≤ 0.8 V across temperature. |
| 5 | D4 | Data input 4 - selected when A=0, B=C=1; maintains <15 ns tPHL to Y under worst-case load conditions. |
| 6 | D5 | Data input 5 - enabled when A=1, B=0, C=1; identical propagation delay to D0–D3 per datasheet switching table. |
| 7 | D6 | Data input 6 - active when A=B=0, C=1; supports 50-pF capacitive loading without signal integrity degradation. |
| 8 | D7 | Data input 7 - selected only when A=B=C=1; full 24-mA IOL capability applies equally across all D inputs. |
| 9 | GND | Ground reference - single ground pin shared by logic core and output drivers; requires low-inductance PCB connection. |
| 10 | Y | True output - provides non-inverted selected data; 3-state controlled by OE; sinks 24 mA when low. |
| 11 | W | Inverted output - complements Y; toggles synchronously with Y; identical timing and drive strength. |
| 12 | OE | Output-enable - active-low control; disables both Y and W simultaneously into high-impedance state. |
| 13 | C | Select bit C - most-significant address line for 3-bit binary decode; VIH/VIL thresholds match all control inputs. |
| 14 | B | Select bit B - middle address line; exhibits same AC loading and setup/hold timing as A and C. |
| 15 | A | Select bit A - least-significant address line; tPLH/tPHL ≤ 10 ns to Y/W ensures deterministic bus turnaround. |
| 16 | VCC | Supply voltage - powers internal logic and output stages; requires local 0.1-µF ceramic decoupling adjacent to pin. |
Key Features
| Feature | Design Value |
|---|---|
| Complementary True/Inverted Outputs | Simultaneous Y and W delivery eliminates need for external inverters in differential bus or parity generation circuits. |
| 3-State Bus Interface | OE-controlled high-impedance mode allows direct connection to shared data buses without contention or external tri-state logic. |
| Full Binary Decoding | Internal A/B/C decoder resolves all eight D inputs without external gating, reducing PCB real estate and propagation delay. |
| ALS Family Performance | Guaranteed 10-ns minimum tPLH to Y at 50-pF load enables use in high-speed control sequencers and address multiplexers. |
| TTL-Compatible Input/Output | VIH/VIL and VOH/VOL thresholds align with 74LS/74F families, enabling drop-in replacement in legacy designs without redesign. |
Applications
| Microprocessor Address Decoding | Legacy Bus Arbitration |
|---|---|
Use Scenario: Selecting memory-mapped peripheral addresses in 8-bit microprocessor systems (e.g., Z80, 8085) where address lines A0–A2 drive SN74ALS251D select inputs. IC Role / Device Role / Timing Role: Acts as address-space demultiplexer, routing chip-select signals to up to eight peripherals based on low-order address bits. Use Value: Eliminates discrete gate arrays; reduces address decode latency to ≤15 ns, preserving critical timing margins in 4-MHz CPU cycles. | Use Scenario: Managing shared data bus access among multiple DMA controllers or co-processors in industrial PLC backplanes. IC Role / Device Role / Timing Role: Functions as bidirectional bus switch controller, using OE to isolate inactive masters and prevent bus contention. Use Value: Enables deterministic bus turnaround with 10-ns enable/disable times, ensuring sub-200-ns arbitration windows for real-time I/O response. |
| Parallel-to-Serial Data Conversion | Logic State Monitoring |
Use Scenario: Converting parallel status flags (e.g., sensor alarms, fault indicators) into serial stream for UART or shift-register input in embedded diagnostics. IC Role / Device Role / Timing Role: Serves as programmable data multiplexer, with external counter driving A/B/C to scan D0–D7 sequentially. Use Value: Reduces GPIO count by 7:1; maintains signal integrity with 24-mA drive strength across long PCB traces to UART RX pins. | Use Scenario: Real-time monitoring of multiple digital control signals (e.g., motor enable, limit switches, safety interlocks) in CNC motion controllers. IC Role / Device Role / Timing Role: Provides synchronized sampling of 8-bit status word via common clock edge on A/B/C, with Y/W feeding comparator or latch inputs. Use Value: Delivers simultaneous true/inverted outputs for redundant validation logic, improving functional safety compliance without added components. |
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 (8-mA IOL), slower speed (tPHL ≤ 25 ns), same pinout and function. | Acceptable where bus loading is light and timing budget permits +10 ns delay; not suitable for 50-MHz bus interfaces. | Choose for cost-sensitive, low-speed replacements where ALS performance headroom is unnecessary. |
| SN74HC251N | CMOS technology, wider VCC range (2–6 V), lower ICC (<8 µA), but 3.3-V logic thresholds and 7.5-mA drive. | Requires level translation in 5-V TTL systems; unsuitable for direct bus driving without buffer; ideal for low-power 3.3-V designs. | Choose only in new 3.3-V designs or with explicit level-shifting; avoid in legacy 5-V TTL bus environments. |
Compared with SN74ALS251D, SN74LS251N offers lower cost and identical footprint but sacrifices 3× drive strength and 40% speed; SN74HC251N enables modern low-voltage operation yet introduces interface incompatibility in existing 5-V systems due to threshold and drive mismatches.
Availability
SN74ALS251D is available at Aetrix Electronics and suitable for industrial control panels, legacy test equipment refurbishment, and military-grade system sustainment requiring stable component supply across extended product lifecycles.
Supply support for SN74ALS251D 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 solutions with over 90 years of innovation in industrial, automotive, and communications markets.
The SN74ALS251D belongs to TI's Advanced Low-Power Schottky (ALS) logic family, engineered for high-speed, low-power TTL-compatible digital systems where robust noise immunity and bus-driving capability were critical design requirements.
FAQ
What is the maximum clock frequency supported by SN74ALS251D in a data selection application?
The SN74ALS251D does not operate on a clock signal - it is asynchronous. Its usable data rate is determined by propagation delay: with tPHL ≤ 15 ns and tPLH ≤ 10 ns to output Y under loaded conditions, it supports reliable operation in systems with bus cycle times ≥ 30 ns, corresponding to effective throughput up to ~33 MHz in tightly timed multiplexed data paths. The SN74ALS251D datasheet confirms no internal clocking element.
Does SN74ALS251D support hot-swap or live-insertion into a powered bus?
No, SN74ALS251D is not hot-swap rated. Its absolute maximum ratings specify VI ≤ 7 V and disabled output voltage tolerance of only 5.5 V. Inserting the SN74ALS251D into a live 5-V bus risks exceeding these limits during pin engagement, potentially damaging input structures. Always power-cycle the system before replacing the SN74ALS251D.
Can SN74ALS251D drive a 50-pF transmission line directly without termination?
Yes - the SN74ALS251D is characterized with CL = 50 pF in its switching specifications, and its 24-mA low-level output drive ensures clean edges into that load. However, for trace lengths >2 inches on FR-4 PCBs, series termination (e.g., 33 Ω at source) is recommended to suppress reflections. The SN74ALS251D output stage is robust enough to handle this standard test condition without waveform degradation.
Is there a pin-compatible replacement for SN74ALS251D with extended temperature range?
No direct pin-compatible replacement exists for the SN74ALS251D in extended temperature range. The SN54ALS251J (−55°C to 125°C) uses the same 16-pin CDIP package but differs mechanically from the SOIC-16 SN74ALS251D. No TI device combines ALS speed, SOIC-16 packaging, and extended temperature rating - the SN74ALS251D remains the sole commercial-grade SOIC option in this family.
What is the quiescent current draw of SN74ALS251D when outputs are disabled?
When outputs are disabled (OE = HIGH), the SN74ALS251D draws ICC ≤ 14 mA at VCC = 5.5 V and all inputs held at 4.5 V, per the "Disabled" row in the recommended operating conditions table. This represents worst-case static supply current - actual consumption drops to ~9.4 mA under typical 0-V/5-V input conditions, confirming efficient 3-state power gating in the SN74ALS251D design.
SN74ALS251D Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 16-SOIC (0.154", 3.90mm Width)
- Packaging:
- Bulk
- Product Status:
- Obsolete
- 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:
- Surface Mount
- Supplier Device Package:
- 16-SOIC
SN74ALS251D FAQ
1.How can I place an order for SN74ALS251D through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS251D 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 SN74ALS251D reliable?
The price and inventory of SN74ALS251D are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS251D is usually 5 days.
3.What payment methods are accepted for SN74ALS251D?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS251D transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS251D?
SN74ALS251D orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS251D 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 SN74ALS251D?
For technical support, including SN74ALS251D datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS251D requirements.
6.How does Aetrix verify that SN74ALS251D is sourced from the original manufacturer or authorized distributors?
All SN74ALS251D 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 SN74ALS251D meets industry standards.
7.What is the process for return or replacement of SN74ALS251D?
All SN74ALS251D units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS251D, 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 SN74ALS251D part is unused and in its original packaging.
Return procedure for SN74ALS251D:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
SN74ALS251D Tags
-
SN74HC138DR
Texas Instruments
-
TC7SB3157CFU,LF(CT
Toshiba Semiconductor and Storage
-
74CBTLV3257PW,118
Nexperia USA Inc.
-
SN74CBTLV3257PWR
Texas Instruments
-
74CBTLV3257GUX
Nexperia USA Inc.
-
74HC154BQ,118
Nexperia USA Inc.
-
P3S0200GMX
NXP USA Inc.
-
SN74CB3Q3245PWR
Texas Instruments
-
SN74CB3Q3257RGYR
Texas Instruments
-
TCA9543APWR
Texas Instruments
-
TCA9546APWR
Texas Instruments
-
SN74HC138N
Texas Instruments
Tech Hub
A practical engineering guide to 3.3V and 5V logic compatibility, input thresholds, resistor dividers, translator ICs, MOSFET level shifting, I2C pull-ups, timing limits and power-sequencing risks.
The 74HC595 uses push-pull logic outputs, while the TPIC6B595 uses 50 V open-drain DMOS sinks for higher-power loads. This guide compares timing, current limits, 3.3 V interfacing, load wiring, thermal…
The 74HC595 converts serial data into eight stable parallel outputs. This guide covers pin functions, shift and storage timing, OE and MR behavior, drive-current limits, cascading, voltage compatibilit…
A technical comparison of level-sensitive latches and edge-triggered flip-flops, covering timing windows, setup and hold limits, master–slave operation, time borrowing, race-through, HDL inference and…
A D latch stores one bit while Enable controls when data can pass. This reference covers gate-level operation, truth tables, transparency, setup and hold timing, LE versus OE, common ICs and practical …
An SR latch stores one bit through cross-coupled feedback. This engineering reference covers NOR and NAND implementations, truth tables, forbidden-state recovery, gated operation, switch debouncing, fa…
Latch circuits retain one bit through feedback. This technical reference covers SR and D latches, truth tables, transparency, timing limits, latch-versus-flip-flop behavior, applications and common log…
An engineering guide to LED driver operation, constant-current and constant-voltage outputs, linear and switching topologies, dimming, IC selection, calculations, replacement compatibility, and fault c…
Operational amplifier guide covering op amp basics, feedback, ideal vs real op amps, common configurations, buffer circuits, offset, bias current, gain-bandwidth, slew rate, rail-to-rail limits and sel…
Jumper cables guide covering safe connection order, red and black clamp placement, final ground connection, cable gauge, length, clamp quality, copper vs CCA cables, jump starter comparison and battery…
