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Texas Instruments SN74ALS257AD
- Part No.:
- SN74ALS257AD
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 16-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
SN74ALS257AD.pdf
- Description:
- IC MULTIPLEXER 4 X 2:1 16SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:369
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Product details
Overview
SN74ALS257AD from Texas Instruments is a quad 2-line-to-1-line data selector/multiplexer with 3-state outputs, designed for bus-organized systems requiring high-performance signal routing. It features 4-bit multiplexing, output-enable (OE) control, and operates over 0°C to 70°C with 5 V supply. Used in legacy industrial control backplanes and microprocessor system buses where bus isolation and source selection are critical.
For engineers reviewing the SN74ALS257AD datasheet, SN74ALS257AD pinout, SN74ALS257AD application, or SN74ALS257AD equivalent, key selection criteria include propagation delay (max 10 ns A/B→Y), 3-state output drive capability (24 mA sink), input voltage thresholds (VIH = 2 V, VIL = 0.8 V), and SOIC-16 package compatibility with legacy PCB layouts.
Technical Context
This device implements four independent 2:1 multiplexers sharing a common A/B select line and output-enable (OE) control. Each channel selects between two 4-bit data sources (A or B) and drives a dedicated 3-state output (1Y–4Y), enabling clean bus arbitration without contention.
Logic operation follows positive-true enable: OE low enables outputs; OE high places all Y outputs in high-impedance state. Input thresholds and switching characteristics are specified for ALS family performance-faster than standard TTL but with lower power than AS variants-making it suitable for mixed-logic-system interfacing.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage (VCC) | 4.5 V to 5.5 V - compatible with standard 5 V logic rails; absolute max 7 V prevents damage during transient overvoltage. |
| Propagation Delay (tPLH/tPHL) | 2–10 ns (A/B → Y) - ensures sub-100 MHz bus timing margins in synchronous control applications. |
| Output Drive (IOL/IOH) | 24 mA sink / −2.6 mA source - sufficient to drive multiple TTL loads or terminate short stubs on shared data buses. |
| Input Thresholds (VIH/VIL) | 2.0 V min VIH / 0.8 V max VIL - guarantees reliable recognition of TTL-compatible logic levels across temperature. |
| 3-State Enable Time (tPZH/tPLZ) | 4–16 ns (OE → Y) - supports fast bus turnaround in time-multiplexed architectures like memory/data bus sharing. |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade embedded systems including industrial HMIs and test equipment. |
| Package | SOIC-16 (D package) - surface-mount footprint with 1.27 mm pitch; compatible with automated assembly and legacy rework workflows. |
Pinout & Package
SN74ALS257AD uses a 16-pin SOIC (D) package with 1.27 mm lead pitch and 7.5 mm body width. Pin numbering follows standard DIP/SOIC convention with Pin 1 in top-left corner (quadrant Q1).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (A/B) | Select control input | Common 2:1 selector for all four channels: logic low routes A inputs to outputs; high routes B inputs. |
| 2–5 (1A–4A) | Data input A group | Four independent data lines from first 4-bit source; routed to corresponding Y outputs when A/B = L. |
| 6–9 (1B–4B) | Data input B group | Four independent data lines from second 4-bit source; routed to corresponding Y outputs when A/B = H. |
| 10–13 (1Y–4Y) | 3-state output group | Active-low enabled outputs; high-impedance when OE = H; driven low/high per selected input when OE = L. |
| 14 (OE) | Output-enable input | Active-low global enable: OE = L activates all Y outputs; OE = H disables all outputs to prevent bus loading. |
| 15 (GND) | Ground reference | Primary return path for logic and output currents; must be low-impedance connection to minimize noise coupling. |
| 16 (VCC) | Power supply | +5 V supply rail; requires local 0.1 µF ceramic decoupling near Pin 16 to suppress switching transients. |
Key Features
| Feature | Design Value |
|---|---|
| 3-State Outputs | Enables direct connection to shared data buses without external pull-ups or contention risk during disable. |
| Bus Interface Capability | Designed specifically for high-performance bus-organized systems-supports clean source switching in microprocessor address/data paths. |
| ALS Logic Family | Combines TTL-compatible voltage levels with improved speed-power trade-off vs. standard 74LS: ~2× faster than LS at similar current draw. |
| Standard Pinout Compatibility | Matches industry-standard 16-pin DIP/SOIC layout used by SN74LS257, SN74AS257, and SN74ALS258-enabling drop-in replacement in many designs. |
| Industrial Temperature Range | Rated for 0°C to 70°C operation-validated for use in non-automotive industrial environments including PLC I/O modules and instrumentation backplanes. |
Applications
| Microprocessor System Bus | Legacy Industrial Backplane |
|---|---|
|
Use Scenario: Multiplexing address/data signals between CPU and multiple peripheral controllers on a shared 4-bit bus. IC Role / Device Role / Timing Role: Quad 2:1 selector routing either primary or secondary peripheral data streams onto common bus lines under software-controlled A/B and OE. Use Value: Eliminates need for discrete gating logic; enables dynamic resource allocation with <10 ns propagation delay and guaranteed bus isolation. |
Use Scenario: Isolating diagnostic test signals from operational control signals in modular rack-mounted I/O systems. IC Role / Device Role / Timing Role: 3-state-enabled multiplexer selecting between production-mode and service-mode data paths while maintaining bus integrity. Use Value: Prevents signal contention during field diagnostics; OE control allows hot-swap-safe insertion/removal of test modules without powering down main system. |
| Programmable Logic Interface | Test Equipment Signal Routing |
|
Use Scenario: Interfacing FPGA configuration data streams with multiple PROM sources in reconfigurable logic systems. IC Role / Device Role / Timing Role: Selecting between boot PROM and update PROM using A/B control, with OE synchronized to FPGA reset sequence. Use Value: Supports dual-image firmware updates without external logic; ALS speed ensures setup/hold timing compliance with FPGA configuration clocks. |
Use Scenario: Routing calibrated reference signals between precision DACs and multiple analog measurement channels in benchtop multimeters. IC Role / Device Role / Timing Role: Low-noise, high-Z multiplexer isolating reference paths during channel scanning to avoid crosstalk-induced offset errors. Use Value: 24 mA sink capability drives heavy capacitive loads; 3-state disable eliminates leakage paths that degrade DC accuracy in µV-range measurements. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar data selector/multiplexer applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS257AN | Same logic function, electrical specs, and pinout-but in 16-pin PDIP (N) package instead of SOIC (D). | Used where through-hole assembly or socket-based prototyping is required; lacks surface-mount thermal and density advantages. | Select SN74ALS257AN for breadboarding, repair, or legacy through-hole production; SN74ALS257AD preferred for volume SMT manufacturing. |
| SN74AS257D | Faster propagation (1–5.5 ns vs. 2–10 ns) and higher drive (48 mA sink), but higher ICC (19.7 mA vs. 14 mA) and reduced noise margin (VIH = 2 V same, but VIL = 0.8 V vs. 0.7 V). | Suitable for high-speed bus arbitration where timing closure is critical; less tolerant of marginal input noise or degraded signal integrity. | Choose SN74AS257D only when sub-5 ns delay is mandatory; SN74ALS257AD offers better power/noise trade-off for general-purpose bus interface. |
Compared with SN74ALS257AN and SN74AS257D, SN74ALS257AD delivers optimal balance of speed, drive strength, and power efficiency in SOIC packaging-making it the preferred choice for new SMT designs requiring proven ALS-family reliability without AS-level complexity.
Availability
SN74ALS257AD is available at Aetrix Electronics and suitable for industrial control backplanes, microprocessor bus interfaces, and programmable logic configuration systems requiring stable component supply and long-term obsolescence management.
Supply support for SN74ALS257AD 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 and automotive qualification.
SN74ALS257AD belongs to TI's legacy 74ALS logic family-designed for high-reliability, medium-speed digital interfacing in commercial and industrial systems where robustness and pin compatibility outweigh cutting-edge speed.
FAQ
What is the maximum operating frequency supported by SN74ALS257AD?
SN74ALS257AD does not specify a maximum clock frequency directly, but its worst-case propagation delay (tPHL/tPLH) is 10 ns for A/B→Y paths and 22 ns for OE→Y transitions. This supports reliable operation up to approximately 50 MHz in well-terminated, low-capacitance bus environments. For SN74ALS257AD, design margin should account for temperature variation and load capacitance-TI recommends limiting data rate to ≤30 MHz for robust timing closure across full temperature range.
Can SN74ALS257AD drive standard TTL loads directly?
Yes, SN74ALS257AD can drive standard TTL loads directly: its IOL rating of 24 mA exceeds the 1.6 mA per input required for seven standard TTL gates (fan-out of 15), and its VOH minimum of 2.4 V meets TTL VIH requirements. For SN74ALS257AD, this capability enables direct connection to legacy 74LS/74S devices without level-shifting or buffering-critical in mixed-logic retrofits and industrial controller upgrades.
Is SN74ALS257AD RoHS compliant?
Yes, SN74ALS257AD is RoHS compliant. Per TI's Package Option Addendum, the active orderable variant SN74ALS257ADR.A carries "Yes" for RoHS status, uses NiPdAu (NIPDAU) lead finish, and is rated Level-1-260°C-UNLIM for moisture sensitivity. For SN74ALS257AD, this confirms full compliance with EU Directive 2011/65/EU and related restrictions on hazardous substances in electronics manufacturing.
What is the purpose of the NC pins in SN74ALS257AD?
SN74ALS257AD has no NC (no-connect) pins-the SOIC-16 package uses all 16 pins for functional I/O, power, or ground. Confusion may arise from the FK (LCCC-20) and J (CDIP-16) variants shown in the datasheet, which do include NC pins, but those do not apply to SN74ALS257AD. For SN74ALS257AD, Pin 1 = A/B, Pins 2–5 = 1A–4A, Pins 6–9 = 1B–4B, Pins 10–13 = 1Y–4Y, Pin 14 = OE, Pin 15 = GND, Pin 16 = VCC-no unused terminals.
How does SN74ALS257AD differ from SN74ALS258A?
SN74ALS257AD implements four independent 2:1 multiplexers with one shared A/B select line and one shared OE input. In contrast, SN74ALS258A provides two independent 4:1 multiplexers-each with dedicated select inputs (S0/S1) and separate OE controls. For SN74ALS257AD, this means simpler control logic for parallel 2-source selection, while SN74ALS258A suits applications needing flexible 4-input routing per channel. Pinouts and AC specs also differ, preventing direct substitution.
SN74ALS257AD 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:
- 4 x 2:1
- 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
SN74ALS257AD FAQ
1.How can I place an order for SN74ALS257AD through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS257AD 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 SN74ALS257AD reliable?
The price and inventory of SN74ALS257AD are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS257AD is usually 5 days.
3.What payment methods are accepted for SN74ALS257AD?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS257AD transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS257AD?
SN74ALS257AD orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS257AD 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 SN74ALS257AD?
For technical support, including SN74ALS257AD datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS257AD requirements.
6.How does Aetrix verify that SN74ALS257AD is sourced from the original manufacturer or authorized distributors?
All SN74ALS257AD 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 SN74ALS257AD meets industry standards.
7.What is the process for return or replacement of SN74ALS257AD?
All SN74ALS257AD units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS257AD, 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 SN74ALS257AD part is unused and in its original packaging.
Return procedure for SN74ALS257AD:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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