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Texas Instruments SN74AS257DR
- Part No.:
- SN74AS257DR
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
SN74AS257DR.pdf
- Description:
- IC MULTIPLEXER 4 X 2:1 16SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:4,743
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Product details
Overview
SN74AS257DR 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 5 V supply, delivers ±48 mA output drive, and achieves propagation delays as low as 1 ns (tPHL/tPLH on A/B→Y). It is used in digital logic subsystems where multiple data sources must be selectively gated onto shared data lines.
For engineers reviewing the SN74AS257DR datasheet, SN74AS257DR pinout, SN74AS257DR application, or SN74AS257DR equivalent, key selection criteria include its 3-state bus interface capability, AS-family speed-performance trade-off (vs. ALS/LS), output current rating (IOL = 48 mA), and compatibility with standard 16-pin SOIC (D) packaging for PCB layout reuse in legacy TTL-compatible designs.
Technical Context
The SN74AS257DR implements two independent 2:1 multiplexers per package, each selecting between two 4-bit inputs (A and B) based on the common A/B select line. Its 3-state outputs are controlled by an active-low OE input, enabling direct connection to system buses without loading when disabled.
It belongs to the 74AS logic family, optimized for higher speed than 74ALS while maintaining TTL-compatible voltage thresholds (VIH = 2 V, VIL = 0.8 V) and 5 V operation. Output drive strength (IOL = 48 mA, IOH = −15 mA) supports fan-out to multiple TTL loads and fast edge rates under 50 pF load conditions.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | 74AS - high-speed bipolar TTL with improved speed-power product vs. ALS/LS |
| Supply Voltage (VCC) | 4.5 V to 5.5 V - compatible with standard 5 V TTL rails; absolute max 7 V |
| Propagation Delay (A/B → Y) | 2 ns min / 11 ns max - enables sub-100 MHz clock-domain switching in synchronous logic |
| Output Drive (IOL / IOH) | 48 mA sink / −15 mA source - drives ≥10 standard TTL loads or interfaces directly with 5 V CMOS inputs |
| 3-State Enable Time (tPZL) | 2 ns min / 9.5 ns max - ensures rapid bus release for time-critical arbitration or shared-bus handshaking |
| Operating Temperature | 0°C to 70°C - commercial-grade rating suitable for industrial control panels and office equipment |
| Package | SOIC-16 (D) - 150 mil width, RoHS-compliant NiPdAu lead finish, MSL Level-1 |
Pinout & Package
SN74AS257DR is supplied in a 16-pin small-outline integrated circuit (SOIC-D) package with 1.27 mm pitch, 7.5 mm body width, and 2.00 mm max height. Pin 1 is marked via notch or bevel on the top surface.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1A, 2A, 3A, 4A | Data Input A group | First set of four parallel data inputs; selected when A/B = L |
| 1B, 2B, 3B, 4B | Data Input B group | Second set of four parallel data inputs; selected when A/B = H |
| 1Y, 2Y, 3Y, 4Y | 3-State Output | Corresponding multiplexed outputs; high-impedance when OE = H |
| A/B | Select Control | Global 2:1 select line - determines whether A or B inputs pass to outputs |
| OE | Output Enable | Active-low enable - disables all outputs (3-state) when high |
| VCC | Power Supply | +5 V supply pin (Pin 16); requires local 0.1 µF decoupling |
| GND | Ground Reference | Signal and power ground (Pin 8); critical for noise immunity and timing stability |
Key Features
| Feature | Design Value |
|---|---|
| 3-State Outputs | Enables direct connection to shared data buses without external pull-ups or isolation logic |
| High Sink Current (48 mA) | Drives heavy capacitive loads or multiple TTL inputs without buffering, reducing component count |
| Low Propagation Delay (1–11 ns) | Supports high-throughput data routing in real-time control and instrumentation applications |
| TTL-Compatible Thresholds | VIH = 2 V / VIL = 0.8 V ensures reliable interfacing with legacy 5 V logic families |
| SOIC-16 Packaging | Standard footprint allows drop-in replacement for other 74-series D-packaged multiplexers |
Applications
| Microprocessor Bus Arbitration | Digital Test Equipment Signal Routing |
|---|---|
Use Scenario: Multiple peripheral controllers compete for access to a shared 4-bit data bus in an 8080/8085-based system. IC Role / Device Role / Timing Role: SN74AS257DR acts as a bidirectional bus switch controller, selecting between master and slave data paths under CPU arbitration logic. Use Value: Its 9.5 ns max disable time (tPZL) ensures clean bus release before next cycle, preventing contention glitches. | Use Scenario: Automated test fixture routes stimulus signals from one of two pattern generators to a DUT's 4-bit port. IC Role / Device Role / Timing Role: SN74AS257DR serves as a programmable signal path selector, controlled by FPGA GPIO lines. Use Value: 48 mA output drive handles 50 Ω transmission line termination and maintains signal integrity up to 50 MHz. |
| Industrial PLC I/O Expansion | Legacy Instrumentation Data Multiplexing |
Use Scenario: Modular PLC backplane aggregates sensor data from two 4-bit analog front-end modules into a single ADC interface. IC Role / Device Role / Timing Role: SN74AS257DR functions as a hardware-multiplexed data concentrator, synchronized to the main scan clock. Use Value: 3-state outputs isolate inactive modules, eliminating crosstalk and reducing power supply noise coupling. | Use Scenario: Oscilloscope front-end selects between internal calibration reference and external probe input for 4-bit trigger logic. IC Role / Device Role / Timing Role: SN74AS257DR provides glitch-free analog-digital boundary switching via synchronized OE control. Use Value: Sub-10 ns propagation delay ensures trigger timing alignment within ±1 ns across channels. |
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 |
|---|---|---|---|
| SN74ALS257ADR | Slower (max tPHL = 12 ns), lower drive (IOL = 24 mA), same pinout and function | Suitable for cost-sensitive, lower-speed systems where 74AS speed is unnecessary | Choose for reduced power consumption (ICC = 19.7 mA vs. 31.9 mA at VCC = 5.5 V, outputs disabled) |
| SN74HC157DR | CMOS technology, wider VCC range (2–6 V), lower drive (IOL = 4 mA), higher input impedance | Better for battery-powered or mixed-voltage systems; not TTL-compatible | Choose only if interfacing with 3.3 V logic or requiring ultra-low static current (ICC < 1 µA) |
Compared with SN74ALS257ADR and SN74HC157DR, the SN74AS257DR delivers the highest speed and drive strength in a TTL-compatible 16-pin SOIC package, making it optimal for legacy 5 V bus architectures demanding deterministic timing and robust noise margins.
Availability
SN74AS257DR is available at Aetrix Electronics and suitable for industrial control panels, test equipment signal routing, and legacy microprocessor bus expansion requiring stable component supply and long-term obsolescence management.
Supply support for SN74AS257DR 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 SN74AS257DR belongs to TI's 74AS logic family, engineered for high-speed digital signal routing in 5 V TTL systems where propagation delay and output drive are critical - particularly in bus arbitration, test instrumentation, and real-time control.
FAQ
What logic family does SN74AS257DR belong to, and how does it differ from 74LS or 74ALS?
SN74AS257DR belongs to the 74AS (Advanced Schottky) logic family. It offers faster propagation delays (1–11 ns) and higher output drive (48 mA sink) than 74ALS (2–12 ns, 24 mA) or 74LS (15–35 ns, 8 mA), at the cost of higher power consumption. Unlike 74HC, it is strictly 5 V TTL-compatible with fixed VIH/VIL thresholds and no wide-supply flexibility.
Does SN74AS257DR support hot-swap or live insertion into a powered bus?
No - SN74AS257DR is not hot-swap rated. Its absolute maximum input voltage is 7 V, and applying signals before VCC stabilization may cause latch-up or damage. Always power VCC before asserting inputs or OE. For hot-swap applications, add series current-limiting resistors and ensure strict power sequencing per TI Application Report SCBA005.
Can SN74AS257DR be used with 3.3 V logic levels?
Not directly. SN74AS257DR requires 4.5–5.5 V VCC and has TTL input thresholds (VIH = 2 V min, VIL = 0.8 V max). While 3.3 V outputs may meet VIH margin, they risk marginal noise immunity. For 3.3 V systems, use level translators or select 74LVC157 instead. SN74AS257DR itself must be powered at 5 V.
What is the recommended decoupling for SN74AS257DR in high-speed layouts?
Place a 0.1 µF ceramic capacitor between VCC (Pin 16) and GND (Pin 8) as close as possible to the device - ideally within 5 mm trace length. For boards with multiple SN74AS257DRs, add a bulk 4.7 µF tantalum capacitor per 4–6 devices. Avoid shared vias between decoupling caps and GND planes to minimize ground bounce.
Is SN74AS257DR pin-compatible with SN74LS257 or SN74ALS257?
Yes - SN74AS257DR shares identical pinout, function table, and package (SOIC-16) with SN74LS257N, SN74ALS257ADR, and SN74ALS257AN. It is a direct speed upgrade: same A/B select, OE control, and 1A–4B/1Y–4Y mapping. No PCB changes are required when replacing these parts in existing designs.
SN74AS257DR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74AS
- Package/Case:
- 16-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- 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:
- Surface Mount
- Supplier Device Package:
- 16-SOIC
SN74AS257DR FAQ
1.How can I place an order for SN74AS257DR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74AS257DR 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 SN74AS257DR reliable?
The price and inventory of SN74AS257DR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74AS257DR is usually 5 days.
3.What payment methods are accepted for SN74AS257DR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74AS257DR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74AS257DR?
SN74AS257DR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74AS257DR 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 SN74AS257DR?
For technical support, including SN74AS257DR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74AS257DR requirements.
6.How does Aetrix verify that SN74AS257DR is sourced from the original manufacturer or authorized distributors?
All SN74AS257DR 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 SN74AS257DR meets industry standards.
7.What is the process for return or replacement of SN74AS257DR?
All SN74AS257DR units undergo pre-shipment inspection (PSI). If there is an issue with SN74AS257DR, 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 SN74AS257DR part is unused and in its original packaging.
Return procedure for SN74AS257DR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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