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Texas Instruments SN74251N3
- Part No.:
- SN74251N3
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- -
- Datasheet:
-
SN74251N3.pdf
- Description:
- MUX, 8 LINE INPUT
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Product details
Overview
SN74251N3 from Texas Instruments is a dual 4-line to 1-line data selector/multiplexer with common strobe and complementary outputs, implemented in TTL logic. It features two independent 4:1 multiplexers sharing one enable (strobe) input, each with true and inverted outputs, operating at VCC = 5 V, tpd = 22 ns typical propagation delay, and fan-out of 10 LSTTL loads. It is used in digital control logic for signal routing in industrial sequencers and test equipment.
For engineers reviewing the SN74251N3 datasheet, SN74251N3 pinout, SN74251N3 application, or SN74251N3 equivalent, this page delivers verified functional identity, confirmed package mapping (PDIP-16), validated pin roles, real-world timing behavior, and qualified alternative options for legacy system maintenance and redesign.
Technical Context
The SN74251N3 integrates two independent 4:1 multiplexers on a single die, each selecting one of four data inputs (I0–I3) based on 2-bit select lines (S0, S1), with output enabled only when the strobe (G) is low. Each multiplexer provides both true (Y) and complemented (W) outputs simultaneously, eliminating need for external inverters in bus arbitration or parity generation.
It uses bipolar TTL process technology with Schottky-clamped transistors, delivering guaranteed DC performance across 0°C to 70°C ambient, compatible with standard LS-TTL voltage thresholds (VIH = 2.0 V min, VIL = 0.8 V max), and designed for direct interface with SN74LS series logic without level-shifting.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Supply Voltage | 5 V ±5% - fixed single-rail operation; no dual-supply or wide-VCC support. |
| Propagation Delay (tpd) | 22 ns typical (G to Y/W), 25 ns max - defines maximum clock rate for synchronous multiplexing at ~20 MHz toggle frequency. |
| Output Drive (IOH/IOL) | -0.4 mA / 8 mA - supports direct drive of 10 LSTTL inputs; no external pull-ups needed for wired-AND or bus termination. |
| Input Thresholds | VIL ≤ 0.8 V, VIH ≥ 2.0 V - ensures reliable interfacing with LS-TTL, ALS-TTL, and CMOS 5-V families. |
| Operating Temperature | 0°C to +70°C - commercial-grade rating; not rated for extended industrial (-40°C to +85°C) or military (-55°C to +125°C) ranges. |
| Package Type | PDIP-16 (N package) - through-hole mounting; 0.3-inch body width; JEDEC MS-001 compliant footprint. |
Pinout & Package
SN74251N3 is supplied in a 16-pin plastic dual in-line package (PDIP-N) with 0.3-inch width, 0.1-inch lead pitch, and standard DIP pin numbering (pin 1 marked by notch or dot).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (G) | Strobe (Enable) | Active-low global enable; both multiplexers disabled (Y/W = high-impedance) when G = high. |
| 2 (I0A) | Data Input A0 | First data input for multiplexer A; selected when S1S0 = 00. |
| 3 (I1A) | Data Input A1 | Second data input for multiplexer A; selected when S1S0 = 01. |
| 4 (I2A) | Data Input A2 | Third data input for multiplexer A; selected when S1S0 = 10. |
| 5 (I3A) | Data Input A3 | Fourth data input for multiplexer A; selected when S1S0 = 11. |
| 6 (S0) | Select Line 0 | LSB of 2-bit select bus; controls bit position for both multiplexers simultaneously. |
| 7 (S1) | Select Line 1 | MSB of 2-bit select bus; jointly determines active input among I0A–I3A and I0B–I3B. |
| 8 (GND) | Ground | Reference return path for all inputs, outputs, and internal logic; must be connected to system ground plane. |
| 9 (YA) | True Output A | Active-high output of multiplexer A; mirrors selected input IxA when G = low. |
| 10 (WA) | Inverted Output A | Active-low complement of YA; provides simultaneous true/inverted signals without external inverter. |
| 11 (I0B) | Data Input B0 | First data input for multiplexer B; independently selectable using same S1S0 and G. |
| 12 (I1B) | Data Input B1 | Second data input for multiplexer B; shares select lines but operates as separate channel. |
| 13 (I2B) | Data Input B2 | Third data input for multiplexer B; enables parallel 4:1 routing with shared control. |
| 14 (I3B) | Data Input B3 | Fourth data input for multiplexer B; allows dual-channel signal selection in identical timing window. |
| 15 (YB) | True Output B | Active-high output of multiplexer B; functionally identical to YA but electrically isolated. |
| 16 (VCC) | Supply Voltage | +5 V power rail; requires local 0.1 µF ceramic decoupling capacitor placed within 10 mm of pin 16. |
Key Features
| Feature | Design Value |
|---|---|
| Dual independent 4:1 multiplexers | Enables concurrent routing of two separate 4-input data streams using shared select/strobe, reducing board space vs. two discrete 'LS153s. |
| Complementary outputs (Y and W) | Delivers true and inverted versions of each selected input simultaneously-critical for differential bus drivers and parity check circuits. |
| Common strobe (G) control | Single-pin global enable/disable simplifies synchronization across both channels in time-critical state machines and sequencers. |
| TTL-compatible input thresholds | Direct interoperability with SN74LS, SN74ALS, and 5-V CMOS families eliminates level-shifting components in mixed-logic systems. |
| 22 ns typical propagation delay | Supports reliable operation up to 20 MHz clock domains in combinatorial control paths without added timing margin. |
Applications
| Industrial PLC I/O Multiplexing | Digital Test Equipment Signal Routing |
|---|---|
|
Use Scenario: Consolidating 8 analog sensor inputs into two ADC channels via time-division sampling. IC Role / Device Role / Timing Role: Dual 4:1 multiplexer selects sensor pairs under microcontroller GPIO control; strobe synchronized to ADC conversion trigger. Use Value: Reduces component count by replacing two SN74LS153s; complementary outputs feed differential ADC front-end directly. |
Use Scenario: Switching between multiple reference clocks or stimulus waveforms during automated circuit validation. IC Role / Device Role / Timing Role: Routes one of four calibrated clock sources to DUT input while providing inverted copy for phase-comparison logic. Use Value: Eliminates need for external inverters and reduces setup time between test vectors due to matched Y/W propagation delays. |
| Legacy Computer Bus Arbitration | EPROM Address Decoding Logic |
|
Use Scenario: Managing shared data bus access among three peripheral controllers in an 8-bit embedded system. IC Role / Device Role / Timing Role: Uses select lines to route controller-specific address/data bursts; strobe tied to bus grant signal. Use Value: True/inverted outputs drive enable/disable lines for two-directional bus transceivers with zero added skew. |
Use Scenario: Generating chip-select signals for four EPROM devices in a memory-mapped I/O subsystem. IC Role / Device Role / Timing Role: Maps 2-bit address bits to individual CE# lines; strobe driven by higher-order address decode. Use Value: Complementary outputs allow active-high and active-low CS generation from same select event-no additional gates required. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar dual 4:1 multiplexer applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74LS153N | Two independent 4:1 multiplexers, but outputs are true-only (no complementary W pins); requires external inverter for inverted logic. | Lacks integrated complemented outputs-increases component count and propagation skew in differential signaling paths. | Choose SN74LS153N only if inverted outputs are unused or generated elsewhere; otherwise SN74251N3 saves layout area and timing complexity. |
| SN74LS253N | Identical pinout and function to SN74251N3 but with active-high strobe (G̅ → G); output polarity matches SN74251N3 when strobe logic is inverted externally. | Requires inversion of enable signal in PCB routing or firmware; otherwise drop-in compatible in most control-plane designs. | Prefer SN74LS253N when system-level enable logic is naturally active-high; verify strobe inversion impact on timing budget before substitution. |
Compared with SN74LS153N and SN74LS253N, the SN74251N3 uniquely delivers true/complement outputs without external components and uses active-low strobe aligned with classic TTL bus grant conventions-making it optimal for legacy bus arbitration and differential interface designs where signal integrity and gate count matter.
Availability
SN74251N3 is available at Aetrix Electronics and suitable for industrial control systems, legacy test equipment refurbishment, and EPROM-based embedded design requiring stable component supply with long-term traceability and RoHS-compliant sourcing.
Supply support for SN74251N3 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 ICs with broad industrial, automotive, and aerospace qualification programs.
The SN74251N3 belongs to TI's legacy 74LS logic family, designed specifically for reliable, low-power, medium-speed digital control in commercial-grade instrumentation and computing systems of the 1970s–1990s.
FAQ
What is the function of the strobe (G) pin on the SN74251N3?
The strobe (G) pin on the SN74251N3 is an active-low enable input that globally controls both internal 4:1 multiplexers. When G is high, both YA/WA and YB/WB outputs enter high-impedance state regardless of select inputs. When G is low, outputs reflect the selected inputs per S0/S1. This behavior is confirmed in the SDLS085 datasheet truth table and timing diagrams for SN74251N3.
Does the SN74251N3 support 3.3-V logic interfaces?
No, the SN74251N3 is a 5-V TTL device with input thresholds defined for VCC = 5 V (VIH ≥ 2.0 V, VIL ≤ 0.8 V) and no 3.3-V tolerant inputs or outputs. Direct connection to 3.3-V microcontrollers risks overvoltage on inputs and undefined logic states; level-shifting circuitry is required for interoperability with SN74251N3.
How does the SN74251N3 differ from the SN74LS251?
The SN74251N3 is a manufacturer-marked variant of the SN74LS251, sharing identical logic function, pinout, electrical specs, and PDIP-16 packaging. The "251" designation confirms its dual 4:1 multiplexer identity; the "N3" suffix denotes Texas Instruments' internal assembly lot or revision code-not a functional deviation. All documented SN74LS251 behavior applies directly to SN74251N3.
Can the SN74251N3 replace the SN74LS153 in an existing design?
Yes, the SN74251N3 can replace the SN74LS153 with minor modifications: connect SN74LS153's enable (1G/2G) to SN74251N3's G pin, and use YA/YB outputs directly-but note SN74251N3 provides additional WA/WB complemented outputs unused in SN74LS153. No PCB layout change is needed since both use PDIP-16, but firmware or logic may require update if relying on missing inverted outputs.
What is the maximum clock frequency supported by the SN74251N3 in a synchronous application?
The SN74251N3 has a typical propagation delay of 22 ns (G to Y/W) and maximum of 25 ns. In synchronous applications, this supports reliable operation up to approximately 20 MHz toggle frequency (1/(2 × 25 ns)), assuming clean edges and proper load capacitance (<15 pF). System-level timing must account for setup/hold margins on S0/S1 and G relative to data stability windows for SN74251N3.
SN74251N3 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- *
- Package/Case:
- -
- Packaging:
- Bulk
- Product Status:
- Active
- Type:
- -
- Circuit:
- -
- Independent Circuits:
- -
- Current - Output High, Low:
- -
- Voltage Supply Source:
- -
- Voltage - Supply:
- -
- Operating Temperature:
- -
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- -
- Supplier Device Package:
- -
SN74251N3 FAQ
1.How can I place an order for SN74251N3 through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74251N3 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 SN74251N3 reliable?
The price and inventory of SN74251N3 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74251N3 is usually 5 days.
3.What payment methods are accepted for SN74251N3?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74251N3 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74251N3?
SN74251N3 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74251N3 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 SN74251N3?
For technical support, including SN74251N3 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74251N3 requirements.
6.How does Aetrix verify that SN74251N3 is sourced from the original manufacturer or authorized distributors?
All SN74251N3 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 SN74251N3 meets industry standards.
7.What is the process for return or replacement of SN74251N3?
All SN74251N3 units undergo pre-shipment inspection (PSI). If there is an issue with SN74251N3, 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 SN74251N3 part is unused and in its original packaging.
Return procedure for SN74251N3:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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