Texas Instruments SN74AHC257BQBR

Overview

SN74AHC257BQBR from Texas Instruments is a quad 2-input data selector/multiplexer with three-state non-inverting outputs, operating across 2V–5.5V V_CC, delivering ≤9.5ns propagation delay at 5V/50pF, and supporting industrial temperature range (–40°C to +125°C). It enables dynamic routing of four independent 2:1 data paths-e.g., selecting between dual 4-bit data sources in microcontroller peripheral interfaces.

For engineers reviewing the SN74AHC257BQBR datasheet, SN74AHC257BQBR pinout, SN74AHC257BQBR application, or SN74AHC257BQBR equivalent, key selection criteria include its shared A/B select logic, active-low 3-state OE control, WQFN-16 (3.6mm × 2.6mm) package with thermal pad, and guaranteed latch-up immunity (>250mA per JESD 17).

Technical Context

The SN74AHC257BQBR implements four independent CMOS-based 2:1 multiplexers sharing common A/B address inputs and a single active-low output-enable (OE) signal. Each channel routes either input A or B to its respective Y output based on the binary state of A/B, while OE globally places all four outputs into high-impedance mode.

All inputs are standard CMOS with ≤10pF input capacitance and rail-to-rail voltage tolerance (–0.5V to V_CC+0.5V); outputs feature balanced drive strength (±8mA at 5V), low dynamic VOL/VOL(P) (≤0.44V/0.8V), and integrated clamp diodes for ESD robustness (HBM ±2000V, CDM ±1000V).

Key Specifications

Pinout & Package

SN74AHC257BQBR uses a 16-pin WQFN (BQB) package measuring 3.6mm × 2.6mm with an exposed thermal pad (pinless, bottom-side). The thermal pad may be connected to GND or left floating; it must not connect to any signal or supply net.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LV257APW and 74AHC257PW, the SN74AHC257BQBR uniquely combines 2V minimum operation, 9.5ns speed at 5V, and WQFN thermal performance - making it optimal for compact, wide-supply industrial controllers requiring deterministic timing and robustness.

Availability

SN74AHC257BQBR is available at Aetrix Electronics and suitable for industrial PLC I/O multiplexing, automotive body control modules, microcontroller peripheral selection, and digital test equipment signal routing requiring stable component supply across extended temperature and voltage ranges.

Supply support for SN74AHC257BQBR 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 decades of expertise in high-reliability logic families and automotive-grade qualification.

The SN74AHC257BQBR belongs to TI's AHC advanced high-speed CMOS logic family, designed specifically for low-power, high-noise-immunity digital interfacing in industrial automation, automotive electronics, and test instrumentation.

FAQ

What is the minimum supply voltage required for reliable operation of the SN74AHC257BQBR?

The SN74AHC257BQBR operates reliably down to 2V V_CC, as specified in its Recommended Operating Conditions. At this voltage, input thresholds scale proportionally (V_IL ≤ 0.5V, V_IH ≥ 1.5V), and output drive remains functional (±50µA), though propagation delay increases. Operation below 2V is not characterized and may result in undefined logic states or failure to meet timing specifications.

Does the SN74AHC257BQBR support hot-swap or live-insertion scenarios?

The SN74AHC257BQBR features rail-to-rail input tolerance (–0.5V to V_CC+0.5V) and integrated clamp diodes, enabling limited hot-swap resilience. However, TI does not characterize or guarantee safe operation during live insertion - proper power sequencing (V_CC established before inputs applied) and current-limiting design are required to prevent latch-up or ESD damage in such applications.

Can unused inputs on the SN74AHC257BQBR be left floating?

No - all unused inputs on the SN74AHC257BQBR must be terminated to either V_CC or GND using direct connection or a 10kΩ pull-up/down resistor. Floating CMOS inputs cause excessive power consumption, oscillation, and potential device malfunction due to indeterminate logic states, as explicitly warned in Section 7.3.2 of the datasheet.

What is the role of the thermal pad on the SN74AHC257BQBR package?

The exposed thermal pad on the SN74AHC257BQBR (BQB package) reduces junction-to-ambient thermal resistance to 105.6°C/W. It may be connected to GND for improved heat dissipation and EMI shielding, or left electrically floating - but must never connect to any signal or supply net other than GND. Solder mask opening and appropriate stencil design are required for reliable thermal pad attachment.

How does the SN74AHC257BQBR handle simultaneous switching of multiple outputs?

The SN74AHC257BQBR exhibits defined dynamic noise characteristics: quiet-output VOL(P) ≤ 0.8V and VOH(V) ≥ 4.4V at 5V, measured with all other outputs switching simultaneously. This ensures signal integrity in bus applications where multiple channels switch in lockstep, provided layout follows TI's guidelines (short traces, ground flood fill, local decoupling).