Texas Instruments SN74F257NSR

Overview

SN74F257NSR from Texas Instruments is a quad 2-line-to-1-line data selector/multiplexer with 3-state outputs, designed for bus interface in TTL-based digital systems. It selects one of two 4-bit data sources (A or B) under A/B control and drives four output lines (Y1–Y4), with output enable (OE) disabling all outputs to high-impedance. Operates at 4.5 V to 5.5 V supply, supports 0°C to 70°C ambient, and delivers tPHL/tPLH ≤ 7 ns typical propagation delay.

For engineers reviewing the SN74F257NSR datasheet, SN74F257NSR pinout, SN74F257NSR application, or SN74F257NSR equivalent, key selection considerations include its 16-pin SOP (NS) package, 3-state bus-driving capability, guaranteed 24 mA low-level output drive, and compatibility with legacy F-series TTL logic families in industrial control backplanes and test equipment signal routing.

Technical Context

The SN74F257NSR implements four independent 2:1 multiplexers sharing common A/B select and OE control inputs. Each channel routes either the A-input or B-input to its corresponding Y-output based on the logic level of A/B, while OE independently enables or disables all Y outputs into high-impedance state - enabling direct connection to shared data buses without external gating.

Its electrical design conforms to standard F-series TTL voltage thresholds (VIL = 0.8 V, VIH = 2.0 V), supports 24 mA sink current per output, and maintains specified switching performance (tPLH/tPHL ≤ 7 ns) across the full operating temperature range (0°C to 70°C) and supply range (4.5 V to 5.5 V).

Key Specifications

Pinout & Package

SOP-16 (NS package), 2.00 mm max height, 16-pin surface-mount small-outline package with gull-wing leads, JEDEC MO-153 compliant, RoHS-compliant NiPdAu lead finish, MSL Level-1.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS257N and SN74HC257DR, the SN74F257NSR provides optimal balance of speed, drive strength, and TTL compatibility for retrofitting or maintaining F-series-based systems - especially where 24 mA sink capability and sub-7 ns propagation are required without changing board layout or logic family.

Availability

SN74F257NSR is available at Aetrix Electronics and suitable for industrial backplane routing, legacy test equipment signal selection, and embedded system address/data multiplexing requiring stable component supply and long-term obsolescence management.

Supply support for SN74F257NSR 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 delivering analog and embedded processing solutions, with over 90 years of innovation in logic, power, and signal chain technologies.

The SN74F257NSR belongs to TI's legacy 74F TTL logic family, engineered for high-speed, robust bus interface in industrial control, instrumentation, and military-grade systems where reliability and deterministic timing are critical.

FAQ

What is the function of the A/B pin on the SN74F257NSR?

The A/B pin on the SN74F257NSR is the common select input for all four 2:1 multiplexers. When A/B is low, the A-inputs (A1–A4) are routed to the Y-outputs (Y1–Y4); when high, the B-inputs (B1–B4) are selected. This single control line synchronizes data source selection across all four channels, simplifying timing-critical bus arbitration logic in the SN74F257NSR.

Does the SN74F257NSR support hot insertion into a live bus?

No - the SN74F257NSR is not hot-swap rated. While its 3-state outputs prevent bus contention when OE is asserted, the device lacks built-in current limiting, slew rate control, or ESD protection beyond standard F-series specifications. Safe insertion requires power sequencing and bus quiescence. For live-insertion applications, external protection circuitry or dedicated hot-swap ICs must be used alongside the SN74F257NSR.

Can the SN74F257NSR operate at 3.3 V supply?

No - the SN74F257NSR requires a minimum VCC of 4.5 V and is not characterized for 3.3 V operation. Its input thresholds (VIH = 2.0 V, VIL = 0.8 V) and output drive are optimized for 5 V TTL systems. Attempting 3.3 V operation may result in marginal noise margins, undefined logic states, or failure to meet timing specs. Use SN74HC257 or SN74LVC257 for 3.3 V–compatible quad multiplexing instead of the SN74F257NSR.

What is the maximum capacitive load the SN74F257NSR can drive reliably?

The SN74F257NSR is characterized for CL = 50 pF in switching tests, with guaranteed tPLH/tPHL ≤ 7 ns under those conditions. While it can drive heavier loads, propagation delay increases linearly with capacitance, and output rise/fall times degrade. For reliable operation beyond 50 pF, derate timing margins and verify setup/hold at the destination - especially when driving multiple TTL inputs or long traces. The SN74F257NSR is not intended for direct transmission-line driving.

Is the SN74F257NSR pin-compatible with other 74F257 package variants?

Yes - the SN74F257NSR uses the same 16-pin SOP (NS) pinout as defined in TI's SDFS065A datasheet for the D and N packages, with identical signal assignments (e.g., Pin 1 = A1, Pin 16 = VCC). However, mechanical dimensions and thermal characteristics differ: NS has 0.65 mm lead pitch vs. D's 1.27 mm, requiring separate PCB footprints. Electrical behavior remains consistent across SN74F257NSR, SN74F257DR, and SN74F257N.