Texas Instruments SN74ALS257ANSR

Overview

SN74ALS257ANSR from Texas Instruments is a quad 2-line-to-1-line data selector/multiplexer with 3-state outputs, designed for bus interface in TTL-compatible digital systems. It features 4-bit multiplexing, output-enable (OE) control, and operates across 0°C to 70°C with V_CC = 4.5–5.5 V. It supports high-performance system bus arbitration in legacy industrial control and instrumentation logic designs.

For engineers reviewing the SN74ALS257ANSR datasheet, SN74ALS257ANSR pinout, SN74ALS257ANSR application, or SN74ALS257ANSR equivalent, key selection considerations include its 16-pin SOP (NS) package, 3-state bus-driving capability, propagation delays down to 2 ns (t_PLH), output drive strength (I_OL = 24 mA), and compatibility with ALS logic family timing and voltage thresholds.

Technical Context

The SN74ALS257ANSR implements four independent 2:1 multiplexers sharing a common A/B select line and output-enable (OE) input. Each Y output is actively driven high or low when enabled, and enters high-impedance state when OE is high - enabling direct connection to shared data buses without external pull-ups or isolation.

Its internal logic follows positive-true enable and select behavior: when OE = L, Y = A if A/B = L, or Y = B if A/B = H. All inputs and outputs conform to ALS TTL electrical specifications, including V_IL ≤ 0.8 V, V_IH ≥ 2.0 V, V_OL ≤ 0.4 V at I_OL = 24 mA, and t_PHL/t_PLH ≤ 12 ns under CL = 50 pF.

Key Specifications

Pinout & Package

SOP (NS) package: 16-pin small-outline plastic package, 2.00 mm max height, 0.65 mm lead pitch, body dimensions 10.4 × 5.4 mm, compliant with JEDEC MS-012.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar data selector applications.

Compared with SN74ALS257AN, SN74ALS257ANSR provides identical logic and timing but enables automated assembly and smaller board area; versus SN74AS257NSR, it trades speed for robustness and lower quiescent current - making it optimal for cost-sensitive, noise-prone industrial control applications.

Availability

SN74ALS257ANSR is available at Aetrix Electronics and suitable for industrial control systems, legacy test equipment upgrades, avionics maintenance interfaces, and telecom line card configurations requiring stable component supply and long-term obsolescence management.

Supply support for SN74ALS257ANSR 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 specializing in analog, embedded processing, and logic solutions with over 50 years of innovation in industrial and automotive electronics.

The SN74ALS257ANSR belongs to TI's legacy ALS TTL logic family, engineered for reliability and interoperability in mission-critical industrial control, instrumentation, and defense systems where long-lifecycle support and proven field performance are essential.

FAQ

What logic family does SN74ALS257ANSR belong to, and how does it differ from standard 74LS?

SN74ALS257ANSR is part of the Advanced Low-Power Schottky (ALS) TTL family. Compared to standard 74LS, it delivers 2× faster propagation (10 ns vs. 20 ns typical), 30% lower power consumption (ICC = 14 mA vs. ~20 mA), and improved noise margins due to tighter V_IH/V_IL thresholds. These enhancements make SN74ALS257ANSR suitable for denser, higher-speed logic designs while maintaining full pin and functional compatibility with LS-series predecessors.

Can SN74ALS257ANSR drive standard TTL loads directly, and what is its fanout capability?

Yes, SN74ALS257ANSR can directly drive standard TTL loads. Its I_OL = 24 mA and I_OH = −1 mA allow it to sink up to 10 standard TTL inputs (each requiring 1.6 mA) or source to 10 LS-TTL inputs (each drawing 0.4 mA). This fanout capability eliminates need for buffer stages in most bus-interface applications, simplifying design and improving signal integrity in multi-drop configurations.

Is SN74ALS257ANSR RoHS-compliant, and what is its moisture sensitivity level?

Yes, SN74ALS257ANSR is RoHS-compliant with NiPdAu lead finish. Its MSL rating is Level-1 at 260°C peak reflow, meaning it has unlimited floor life and requires no baking prior to soldering - ideal for standard SMT assembly lines handling mixed-technology boards with both moisture-sensitive and non-sensitive components.

How does the 3-state output behavior of SN74ALS257ANSR prevent bus contention?

When OE is high, all four Y outputs enter high-impedance (Hi-Z) state with leakage current ≤ ±20 µA, effectively disconnecting them from the bus. This prevents simultaneous driving by multiple devices - a critical feature in shared-bus architectures like industrial backplanes or test equipment signal routing. The fast disable time (t_PLZ ≤ 15 ns) ensures rapid bus release before another device asserts its outputs.

What are the key layout recommendations for SN74ALS257ANSR in high-noise industrial environments?

Place a 0.1 µF ceramic capacitor between V_CC and GND within 2 mm of pins 12 and 10; route GND and V_CC traces as wide, low-inductance planes; keep input traces short and away from noisy switching nodes; and avoid routing OE or A/B select lines parallel to clock or motor-drive traces. These practices maintain noise margins > 0.4 V and prevent false triggering in electrically harsh settings where SN74ALS257ANSR is commonly deployed.