Texas Instruments SN74F257N

Overview

SN74F257N from Texas Instruments is a quad 2-line-to-1-line data selector/multiplexer with 3-state outputs, designed for bus interface in high-performance TTL systems. It features 4-bit multiplexing, active-low output enable (OE), A/B select control, and operates over 0°C to 70°C with VCC = 4.5–5.5 V. It directly interfaces with system buses in legacy computing and industrial control backplanes.

For engineers reviewing the SN74F257N datasheet, SN74F257N pinout, SN74F257N application, or SN74F257N equivalent, key selection criteria include its 16-pin PDIP package, 3-state bus-driving capability, propagation delays under 7 ns, low-level input voltage threshold of 0.8 V, and compatibility with standard 5-V TTL logic families.

Technical Context

The SN74F257N implements four independent 2:1 multiplexers sharing a common A/B select line and a global 3-state output enable (OE). Each Y output reflects either the corresponding A or B input based on the A/B logic level, with high-impedance state asserted when OE is high.

Its switching behavior is characterized under CL = 50 pF and R1/R2 = 500 Ω, delivering tPLH/tPHL ≤ 7 ns for data paths and ≤ 15 ns for select/enable paths. The device complies with ANSI/IEEE Std 91-1984 logic symbol conventions and supports direct connection to loaded data buses without external buffering.

Key Specifications

Pinout & Package

SN74F257N is supplied in a 16-pin plastic dual in-line package (PDIP-N), 300-mil width, with through-hole mounting and standard DIP footprint (0.1" pin pitch). Pin 1 is marked by a notch or dot at the top-left corner.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74F257N, SN74LS257N trades speed and drive for power efficiency, while SN74ACT257N improves both speed and power but introduces CMOS input voltage requirements-neither is pin-compatible without circuit review.

Availability

SN74F257N is available at Aetrix Electronics and suitable for computer backplane design, industrial controller refurbishment, and legacy instrumentation repair requiring stable component supply and long-term obsolescence mitigation.

Supply support for SN74F257N 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 solutions for industrial, automotive, and communications markets.

The SN74F257N belongs to TI's 74F Fast TTL logic family, engineered for high-speed bus interfacing and data routing in commercial-grade computing and control systems where robustness and timing predictability are critical.

FAQ

What is the function of the A/B pin on the SN74F257N?

The A/B pin on the SN74F257N is a common select control that determines which of the two 4-bit input sources (A or B) is routed to the four 3-state outputs. When A/B is low, all Y outputs reflect the corresponding A inputs (1A–4A); when high, they reflect the B inputs (1B–4B). This single-pin control simplifies routing logic in bus-switching applications and is electrically identical across all four channels of the SN74F257N.

Does the SN74F257N support hot-swapping on a live bus?

The SN74F257N supports controlled hot-swap operation when used with proper sequencing: assert OE high before inserting or removing the device to place all outputs in high-impedance state, preventing bus contention. Its absolute maximum input voltage rating (−1.2 V to 7 V) and ±50 µA off-state leakage (IOZL/IOZH) provide margin against transients, but external current-limiting or bus isolation is recommended for uncontrolled hot-plug scenarios involving the SN74F257N.

Can the SN74F257N be used with 3.3-V logic families?

No, the SN74F257N is not compatible with 3.3-V logic families. It requires VCC = 4.5–5.5 V and has TTL input thresholds (VIH = 2.0 V min, VIL = 0.8 V max), making it unsuitable for direct interface with 3.3-V CMOS or LVTTL outputs without level-shifting circuitry. Driving the SN74F257N inputs from 3.3-V sources risks marginal VIH compliance and increased static power; likewise, its 5-V outputs may damage 3.3-V receivers. Use dedicated level translators when integrating the SN74F257N into mixed-voltage systems.

What is the maximum capacitive load the SN74F257N can drive reliably?

The SN74F257N is characterized for reliable operation with CL = 50 pF, as specified in its switching characteristics table. While it can drive heavier loads (e.g., >100 pF) at reduced speed, propagation delays increase nonlinearly beyond this point, and output voltage margins degrade due to IOL limitations (24 mA max). For designs requiring >50 pF loading-such as long traces or multiple TTL inputs-buffering or layout optimization is recommended to maintain timing integrity and noise immunity of the SN74F257N outputs.

Is there a surface-mount version of the SN74F257N available?

Yes, Texas Instruments offers surface-mount variants of the same logic function: SN74F257DR (SOIC-16) and SN74F257NSR (SOP-16). Both share identical electrical specifications, timing, and pinout with the SN74F257N (PDIP-16), differing only in package type and thermal/mechanical characteristics. The SN74F257DR uses a standard SOIC body with gull-wing leads, while the SN74F257NSR employs a narrower SOP outline; both are RoHS-compliant and rated for 0°C to 70°C operation like the SN74F257N.