STMicroelectronics 74AC257MTR

Overview

74AC257MTR from STMicroelectronics is a quad 2-channel non-inverting multiplexer with 3-state outputs, designed for high-speed data routing in digital logic systems. It features 4.5 ns typical propagation delay at 5 V, ±24 mA output drive capability, and operates across 2 V to 6 V supply range. Used in address/data bus selection, signal gating, and test instrumentation where low skew and fast switching are required.

For engineers reviewing the 74AC257MTR datasheet, 74AC257MTR pinout, 74AC257MTR application, or 74AC257MTR equivalent, key selection criteria include guaranteed 50 Ω transmission line driving, symmetrical tPLH/tPHL delays, 3-state enable timing (tPZL/tPLZ), latch-up immunity, and compatibility with standard 74-series logic footprints and function.

Technical Context

The 74AC257 implements four independent 2:1 multiplexers sharing common SELECT and active-low OE inputs. Each channel selects between A- or B-input based on SELECT logic level and drives its Y-output only when OE is LOW; otherwise, outputs enter high-impedance state.

It uses sub-micron C2MOS technology for low ICC (4 µA max) and high noise immunity (VNIH/VNIL ≥ 28% VCC). All I/O pins include 2 kV ESD protection and support 50 Ω transmission line driving with matched |IOH| = |IOL| ≥ 24 mA under load.

Key Specifications

Pinout & Package

TSSOP-16 package (4.9 × 6.4 mm body, 0.65 mm pitch); RoHS-compliant, surface-mount, moisture-sensitive level 1.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74AC257N and 74LVC257PW, the 74AC257MTR uniquely supports full 2–6 V operation in a space-efficient TSSOP package while maintaining 50 Ω line driving and industrial temperature range - making it optimal for mixed-voltage, high-reliability embedded control.

Availability

74AC257MTR is available at Aetrix Electronics and suitable for memory subsystems, automated test equipment, digital audio interfaces, and industrial PLC I/O expansion requiring stable component supply across extended temperature and voltage ranges.

Supply support for 74AC257MTR 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, Switzerland, specializing in automotive, industrial, and power management ICs with vertical manufacturing capabilities.

The 74AC logic family delivers advanced CMOS performance with enhanced noise immunity and latch-up resistance, targeting high-reliability digital control, instrumentation, and legacy-compatible upgrades in harsh environments.

FAQ

What is the maximum operating frequency supported by the 74AC257MTR?

The 74AC257MTR does not specify a maximum clock frequency, but its 4.5 ns typical propagation delay at 5 V implies reliable operation up to approximately 220 MHz in ideal conditions. Actual usable frequency depends on load capacitance, trace impedance, and system-level timing margins - verified via worst-case tPLH/tPHL values across temperature and voltage.

Can the 74AC257MTR interface directly with 3.3 V microcontrollers?

Yes - the 74AC257MTR operates down to 2 V and accepts VIH ≥ 2.1 V at 3.3 V supply, meeting 3.3 V CMOS input thresholds. Its outputs swing rail-to-rail (VOH ≥ 3.2 V, VOL ≤ 0.44 V at 24 mA), ensuring compatible logic levels when powered at 3.3 V. No level-shifting is required.

Is the 74AC257MTR pin-compatible with older 74LS257 devices?

No - while functionally equivalent and pinout-identical (TSSOP-16 matches LS257 DIP-16 pin numbering), the 74AC257MTR has different DC characteristics: higher drive strength (24 mA vs 8 mA), wider VCC range (2–6 V vs 4.75–5.25 V), and CMOS input thresholds. Direct replacement requires verifying voltage compatibility and fan-out loading.

Does the 74AC257MTR require external pull-up or pull-down resistors on SELECT or OE?

No - internal circuitry ensures defined logic states with OE and SELECT left unconnected only if driven by clean CMOS outputs. However, in noisy environments or floating-control scenarios, a 10 kΩ pull-down on OE (to disable outputs by default) and pull-up/pull-down on SELECT (for known default channel selection) is recommended for robust startup behavior.