Texas Instruments SN74ALS257ANS

Overview

SN74ALS257ANS from Texas Instruments is a quad 2-line-to-1-line data selector/multiplexer with 3-state outputs, designed for bus-organized systems. It features 4-bit multiplexing capability, output-enable (OE) control, and operates over 0°C to 70°C with 5 V supply. It interfaces directly with system buses in high-performance digital logic applications such as address/data routing in legacy microprocessor systems.

For engineers reviewing the SN74ALS257ANS datasheet, SN74ALS257ANS pinout, SN74ALS257ANS application, or SN74ALS257ANS equivalent, key selection criteria include its 3-state bus interface capability, propagation delay (tPLH/tPHL ≤ 10 ns), output drive strength (IOL = 12 mA), and compatibility with standard TTL/ALS logic families in industrial control and instrumentation designs.

Technical Context

The SN74ALS257ANS implements four independent 2:1 multiplexers sharing a common A/B select line and output-enable (OE) input. Each Y output is 3-state, disabling all outputs simultaneously when OE is high, enabling clean bus arbitration without external gating.

Its ALS (Advanced Low-Power Schottky) logic family delivers improved speed-power trade-off versus standard LS: typical propagation delay of 8 ns (A/B → Y) and 10 ns (OE → Y) at CL = 50 pF, with ICC ≤ 14 mA when outputs are disabled - critical for low-noise, multi-source bus systems requiring deterministic enable/disable timing.

Key Specifications

Pinout & Package

SN74ALS257ANS is supplied in a 16-pin Small Outline Package (SOP-NS), 2.00 mm max height, 1.27 mm lead pitch, with gull-wing leads and pin 1 identification marking. The package complies with JEDEC MS-012 and is RoHS-compliant with NiPdAu lead finish.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar quad 2:1 multiplexer applications.

Compared with SN74ALS257AN, SN74ALS257ANS offers identical logic performance in a space-saving SOP package ideal for high-density production boards; versus SN74AS257NSR, it trades raw speed for lower power, better noise immunity, and broader voltage margin - making it the preferred choice for stable, cost-sensitive industrial control applications.

Availability

SN74ALS257ANS is available at Aetrix Electronics and suitable for industrial control systems, legacy microprocessor support circuits, and digital instrumentation requiring stable component supply with long-term lifecycle assurance.

Supply support for SN74ALS257ANS 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 SN74ALS257ANS belongs to TI's legacy 74ALS logic family, engineered for high-speed, low-power digital interfacing in bus-organized systems - targeting reliability-critical applications where compatibility with established TTL architectures remains essential.

FAQ

What is the maximum operating frequency supported by the SN74ALS257ANS?

The SN74ALS257ANS does not specify a maximum clock frequency in its datasheet, as it is a combinational logic device without internal clocking. Its usable speed is determined by propagation delay: worst-case tPHL/tPLH is 10 ns (A/B → Y) and 12 ns (OE → Y) at VCC = 4.5–5.5 V and CL = 50 pF. This supports reliable operation in synchronous systems with cycle times ≥ 20 ns (i.e., ≤ 50 MHz effective bus rate), assuming proper board-level timing margins.

Does the SN74ALS257ANS support mixed-voltage operation (e.g., 3.3 V inputs with 5 V supply)?

No, the SN74ALS257ANS is a 5 V-only device with TTL-compatible input thresholds (VIH = 2.0 V min, VIL = 0.8 V max) and absolute maximum input voltage of 7 V. While 3.3 V logic signals may meet VIH/VIL specs under nominal conditions, TI does not characterize or guarantee operation with 3.3 V inputs. For mixed-voltage systems, use a dedicated level translator or a 3.3 V–tolerant logic family like 74LVC.

What is the meaning of "NS" in SN74ALS257ANS and how does it differ from "N" or "D" packages?

The "NS" suffix in SN74ALS257ANS denotes the SOP (Small Outline Package) variant with 1.27 mm lead pitch and gull-wing leads - distinct from "N" (16-pin PDIP, through-hole) and "D" (SOIC, 1.27 mm pitch but different body dimensions and moisture sensitivity level). NS is optimized for fine-pitch surface-mount assembly and has a JEDEC MS-012 compliant outline, whereas "D" is obsolete for this part per TI's packaging addendum.

Can the SN74ALS257ANS be used as a 1-bit wide 4:1 multiplexer?

No - the SN74ALS257ANS is strictly a quad 2:1 multiplexer: each of its four Y outputs selects between only two inputs (e.g., 1Y chooses between 1A and 1B). It lacks independent select lines per channel or cascading capability required for true 4:1 operation. To implement a 4:1 function, external logic (e.g., additional 2:1 stages or a dedicated 4:1 IC like SN74ALS153) is necessary.

Is the SN74ALS257ANS pin-compatible with the SN74LS257 or SN74F257?

Yes, the SN74ALS257ANS is pin-compatible and functionally equivalent to SN74LS257 and SN74F257 in the 16-pin SOP (NS) or PDIP (N) packages, sharing identical pinout, logic function, and DC electrical characteristics. However, ALS offers superior speed (≈2× LS, ≈1.5× F) and lower power than LS, while matching F-series speed with better noise immunity - making it a direct upgrade path where timing margins allow.