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Texas Instruments SN74AS257N
- Part No.:
- SN74AS257N
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74AS257N.pdf
- Description:
- IC MULTIPLEXER 4 X 2:1 16DIP
- Quantity:
- Payment:
- Shipping:
Inventory:2,236
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Product details
Overview
SN74AS257N from Texas Instruments is a 4-bit dual 2-line-to-1 data selector/multiplexer with 3-state outputs, designed for bus-organized systems requiring high-speed signal routing and bus interface capability. It operates from 0°C to 70°C, supports 4.5 V–5.5 V supply, delivers ±48 mA output drive, and achieves propagation delays as low as 1 ns (A/B → Y) and 1.5 ns (OE → Y). It is used in legacy industrial control backplanes and TTL-compatible data path switching.
For engineers reviewing the SN74AS257N datasheet, SN74AS257N pinout, SN74AS257N application, or SN74AS257N equivalent, this page provides verified functional identity, validated timing specs, confirmed package mapping (16-pin PDIP), real-world bus interface use cases, and two technically documented alternative parts with explicit differences in drive strength and propagation delay.
Technical Context
The SN74AS257N implements four independent 2:1 multiplexers sharing a common A/B select line and a single 3-state output-enable (OE) input. Each Y output is actively driven high or low when enabled and presents high-impedance (Z) when OE = HIGH, enabling direct connection to shared data buses without loading.
Its AS-family logic uses advanced Schottky-clamped bipolar technology, delivering higher speed and greater current drive than ALS variants - specifically 48 mA sink and 15 mA source capability at VCC = 5.5 V, with tPLH/tPHL ≤ 6 ns on data paths and ≤ 7.5 ns on enable paths under CL = 50 pF conditions.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | AS (Advanced Schottky) - enables faster switching and stronger drive vs. LS/ALS, critical for noise-immune bus loading in mixed-logic systems. |
| Supply Voltage Range | 4.5 V to 5.5 V - compatible with standard 5 V TTL rails; operation outside this range risks damage or undefined behavior. |
| Output Drive (IOL / IOH) | 48 mA sink / 15 mA source - sufficient to directly drive multiple TTL inputs or terminate short PCB traces without external buffers. |
| Propagation Delay (A/B → Y) | 1 ns (min) to 5.5 ns (max) - supports >100 MHz data path toggling in synchronous bus architectures with tight timing budgets. |
| Enable/Disable Time (OE → Y) | 1.5 ns (min) to 7 ns (max) - ensures clean bus arbitration with minimal glitch window during output state transitions. |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade embedded systems, not extended industrial or automotive environments. |
| Input Compatibility | TTL-level - VIH = 2 V min, VIL = 0.8 V max - interfaces natively with 74-series logic without level-shifting. |
Pinout & Package
SN74AS257N 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 |
|---|---|---|
| 1A, 2A, 3A, 4A | Data Input A (low-order source) | Four independent inputs selected when A/B = LOW; routed to corresponding Y outputs. |
| 1B, 2B, 3B, 4B | Data Input B (high-order source) | Four independent inputs selected when A/B = HIGH; routed to corresponding Y outputs. |
| 1Y, 2Y, 3Y, 4Y | 3-State Output | Active-drive or high-Z output per channel; sinks up to 48 mA or sources up to 15 mA when enabled. |
| A/B | Common Select Line | Single control determining whether A-inputs (LOW) or B-inputs (HIGH) appear at outputs. |
| OE | Output Enable (active LOW) | Drives all Y outputs to high-impedance when HIGH; enables bus sharing across multiple devices. |
| VCC | Positive Supply | 5 V nominal power rail; must be decoupled locally to suppress switching noise. |
| GND | Ground Reference | Return path for all I/O and supply currents; requires low-impedance connection to system ground plane. |
Key Features
| Feature | Design Value |
|---|---|
| 3-State Outputs | Enables direct connection to shared data buses without contention; eliminates need for external bus transceivers in multi-source systems. |
| High-Speed AS Logic | Delivers sub-6 ns propagation delays - 2× faster than ALS equivalents - reducing setup/hold margins in high-clock-rate control logic. |
| Strong Output Drive | 48 mA sink capability allows driving 10+ standard TTL loads or terminating unterminated stubs on backplane traces. |
| Single A/B Select Control | Simplifies PCB layout and reduces FPGA/CPLD pin count by eliminating four separate select lines for quad 2:1 muxing. |
| TTL-Compatible Inputs | Accepts standard 5 V TTL thresholds (VIH ≥ 2 V, VIL ≤ 0.8 V), ensuring interoperability with legacy 74-series and microcontroller GPIOs. |
Applications
| Industrial Backplane Data Switching | Legacy Microprocessor Bus Expansion |
|---|---|
Use Scenario: Routing address/data signals between multiple peripheral cards and a central controller in a modular rack-mounted PLC chassis. IC Role / Device Role / Timing Role: Quad 2:1 multiplexer selecting between primary and backup I/O modules; 3-state outputs isolate inactive paths during hot-swap events. Use Value: Eliminates mechanical switches or relays; enables software-controlled reconfiguration of signal paths with <6 ns latency and no external buffering. | Use Scenario: Adding parallel memory-mapped peripherals (e.g., UART, timer, GPIO) to an 8086/8088-based SBC without modifying the main bus decoder logic. IC Role / Device Role / Timing Role: Data path selector isolating peripheral data lines from the CPU bus during non-access cycles; OE synchronized to bus grant signals. Use Value: Provides deterministic 3-state control with 7 ns enable/disable time - prevents bus contention during DMA or interrupt acknowledge phases. |
| Test Equipment Signal Routing | Digital Logic Analyzer Front-End |
Use Scenario: Multiplexing analog-to-digital converter outputs or sensor channels into a shared digital acquisition path in automated test fixtures. IC Role / Device Role / Timing Role: High-fanout data selector feeding ADC result latches; A/B selects between calibration and measurement modes. Use Value: 48 mA drive ensures clean signal integrity into 50 Ω scope inputs or FPGA input buffers without added termination resistors. | Use Scenario: Capturing multiple synchronous digital signals (e.g., address, control, data) from a target system onto a single LA channel bank via time-division sampling. IC Role / Device Role / Timing Role: Channel selector gated by LA sample clock; 3-state outputs prevent back-driving when LA is idle or in trigger-armed state. Use Value: Sub-6 ns propagation delay preserves signal edge fidelity across 4-channel interleaved capture, supporting >100 MHz effective sampling rates. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar 4-bit 2:1 multiplexer applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS257N | Lower drive (24 mA sink), slower speed (12 ns max A→Y delay), higher ICC (19.7 mA active vs. 30.6 mA for SN74AS257N). | Better suited for low-power, lower-frequency systems where fanout < 5 and timing slack > 10 ns exists. | Select SN74ALS257N only if power budget is constrained and speed requirements are relaxed; not drop-in due to timing and drive mismatch. |
| SN74F257N | F-family: 35 mA sink, 8 ns max A→Y delay, 10 mA ICC active; TTL-compatible but lacks AS-level noise immunity and edge sharpness. | Appropriate for cost-sensitive designs where moderate speed suffices and board-level EMI is controlled. | Choose SN74F257N for legacy F-series compatibility; verify noise margin and bus settling time - not recommended for noisy industrial enclosures. |
Compared with SN74ALS257N and SN74F257N, the SN74AS257N offers superior speed and drive at the cost of higher quiescent current, making it optimal for high-reliability, high-speed bus arbitration where signal integrity and timing margin are critical.
Availability
SN74AS257N is available at Aetrix Electronics and suitable for industrial backplane switching, legacy microprocessor bus expansion, test equipment signal routing, and digital logic analyzer front-end designs requiring stable component supply and long-term obsolescence management.
Supply support for SN74AS257N 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 deep heritage in TTL and bipolar logic families.
The SN74AS257N belongs to TI's Advanced Schottky (AS) logic product line, engineered for high-speed digital systems requiring robust noise immunity, strong bus-driving capability, and compatibility with legacy 5 V TTL infrastructure.
FAQ
What is the maximum operating temperature for SN74AS257N?
The SN74AS257N is characterized for operation from 0°C to 70°C ambient temperature. It is not rated for extended temperature ranges such as −40°C to 85°C or industrial −40°C to 105°C. Operation outside 0°C–70°C may result in parametric failure or reduced reliability. Always maintain PCB-level thermal design within this envelope for SN74AS257N.
Does SN74AS257N support 3.3 V logic inputs?
No, SN74AS257N is a 5 V TTL-family device with VIH(min) = 2.0 V and VIL(max) = 0.8 V. While 3.3 V CMOS outputs often exceed 2.0 V, they may not guarantee consistent high-level recognition across voltage tolerances and temperature. Direct interfacing with 3.3 V logic requires level translation; SN74AS257N itself does not tolerate 3.3 V supply or input-only operation.
Can SN74AS257N replace SN74LS257N in an existing design?
SN74AS257N can functionally replace SN74LS257N in most cases due to identical pinout and logic behavior, but requires validation of timing margins and power delivery. Its faster propagation (≤5.5 ns vs. ≤15 ns) and higher drive (48 mA vs. 8 mA) may cause signal integrity issues or excessive current draw if the original design relied on LS-family slew rate or fanout limits. Review PCB trace lengths and termination before substitution.
What is the purpose of the A/B pin on SN74AS257N?
The A/B pin on SN74AS257N is a common select control that determines which of two 4-bit input groups (A-side or B-side) is routed to the four 3-state outputs (1Y–4Y). When A/B = LOW, inputs 1A–4A pass through; when A/B = HIGH, inputs 1B–4B pass through. This single-line control simplifies routing and reduces control logic complexity versus individual select lines per channel.
Is SN74AS257N RoHS compliant?
Yes, SN74AS257N is RoHS compliant. Per TI's packaging documentation, the N-package variant carries "Yes" in the RoHS column, with lead finish specified as NiPdAu (nickel-palladium-gold), confirming compliance with Directive 2011/65/EU and its amendments. No lead or other restricted substances exceed allowable thresholds in the finished SN74AS257N device.
SN74AS257N Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74AS
- Package/Case:
- 16-DIP (0.300", 7.62mm)
- Packaging:
- Bulk
- Product Status:
- Active
- Type:
- Multiplexer
- Circuit:
- 4 x 2:1
- Independent Circuits:
- 1
- Current - Output High, Low:
- 15mA, 48mA
- 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
SN74AS257N FAQ
1.How can I place an order for SN74AS257N through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74AS257N 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 SN74AS257N reliable?
The price and inventory of SN74AS257N are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74AS257N is usually 5 days.
3.What payment methods are accepted for SN74AS257N?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74AS257N transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74AS257N?
SN74AS257N orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74AS257N 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 SN74AS257N?
For technical support, including SN74AS257N datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74AS257N requirements.
6.How does Aetrix verify that SN74AS257N is sourced from the original manufacturer or authorized distributors?
All SN74AS257N 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 SN74AS257N meets industry standards.
7.What is the process for return or replacement of SN74AS257N?
All SN74AS257N units undergo pre-shipment inspection (PSI). If there is an issue with SN74AS257N, 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 SN74AS257N part is unused and in its original packaging.
Return procedure for SN74AS257N:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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