Texas Instruments SN74S257N

Overview

SN74S257N from Texas Instruments is a quadruple 2-line to 1-line data selector/multiplexer IC used for digital signal routing in TTL-compatible logic systems. It features four independent 2:1 multiplexers, single active-low strobe (G̅), complementary outputs (Y and Y̅), and operates over 0°C to 70°C with typical propagation delay of 5 ns at V_CC = 5 V. It is commonly deployed in address/data bus switching, function generator control, and digital test equipment.

For engineers reviewing the SN74S257N datasheet, SN74S257N pinout, SN74S257N application, or SN74S257N equivalent, this page delivers verified functional specifications, validated PDIP-16 package details, confirmed TTL input/output compatibility, and real-world use context for legacy system maintenance and industrial control design.

Technical Context

The SN74S257N implements four identical 2:1 multiplexer cells sharing a common strobe input (G̅) that enables or disables all outputs simultaneously. Each cell selects between two data inputs (A and B) based on a single select line (S), producing both true (Y) and complemented (Y̅) outputs.

It uses Schottky-clamped TTL circuitry for high-speed operation (t_pd = 5 ns max), supports fan-out of 10 LS-TTL loads, and maintains output drive capability of –20 mA (sink) and 0.4 mA (source) under standard conditions.

Key Specifications

Pinout & Package

SN74S257N is supplied in a 16-pin plastic dual in-line package (PDIP-N), 0.300-inch body width, with 0.100-inch lead pitch. Pin 1 is marked by a notch or dot; leads are straight and tin-plated for solderability.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS257BN and SN74F257N, the SN74S257N delivers optimal balance of speed (5 ns), drive strength, and legacy system compatibility - making it the preferred choice for mid-speed industrial controllers where LS is too slow and F is unnecessarily power-hungry.

Availability

SN74S257N is available at Aetrix Electronics and suitable for industrial control logic, digital test equipment, legacy computer bus interface, and function generator addressing requiring stable component supply and long-term obsolescence support.

Supply support for SN74S257N 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 and embedded processing technologies with broad industrial, automotive, and aerospace product portfolios.

The SN74S257N belongs to TI's legacy 74S TTL logic family, designed specifically for high-speed digital control systems where propagation delay and output drive were prioritized over power efficiency.

FAQ

What is the maximum operating frequency supported by SN74S257N?

The SN74S257N does not specify a maximum clock frequency in its datasheet because it is a combinational logic device without an internal clock. Its usable switching rate depends on propagation delay (5 ns typical) and system-level timing margins. In practice, SN74S257N reliably supports data selection in paths with 20–30 MHz toggle rates when paired with appropriate setup/hold timing from upstream registers.

Can SN74S257N be used with 3.3 V logic systems?

No, SN74S257N is a 5 V-only TTL device requiring V_CC = 4.75–5.25 V. Its input thresholds (V_IH ≥ 2.0 V, V_IL ≤ 0.8 V) and output voltages (V_OH ≈ 2.7 V, V_OL ≈ 0.5 V) are incompatible with 3.3 V CMOS logic levels. Interfacing with 3.3 V systems requires level-shifting buffers or voltage translators - direct connection may cause unreliable operation or damage.

Does SN74S257N have three-state outputs?

No, SN74S257N does not feature three-state (high-impedance) outputs. When the strobe (G̅) is high, all Y outputs are forced low and all Y̅ outputs are forced high - they remain actively driven, not tri-stated. For true high-Z behavior, consider alternatives like SN74LS253 or SN74ALS157 with explicit output-enable pins.

How does the strobe (G̅) pin affect output timing in SN74S257N?

The strobe (G̅) pin overrides all select (S) and data (A/B) inputs: when G̅ = high, Y = low and Y̅ = high regardless of other signals. Propagation delay from G̅ to output is specified separately (t_pd = 4 ns typ), and is faster than data-path delay. This allows precise, glitch-free output blanking synchronized to system control signals - essential in bus arbitration and test-mode isolation.

Is SN74S257N pin-compatible with SN74LS257N or SN74F257N?

Yes, SN74S257N shares identical pinout, package (PDIP-16), and terminal functions with SN74LS257N and SN74F257N. All three devices route G̅, A/B inputs, Y/Y̅ outputs, V_CC, and GND to the same pins. This allows drop-in substitution in existing PCB layouts - though timing, drive strength, and power must be re-verified per application requirements.