Texas Instruments SN74AHCT257BQBR

Overview

SN74AHCT257BQBR from Texas Instruments is a quad 2-input data selector/multiplexer with three-state non-inverting outputs, operating at 4.5V–5.5V V_CC, delivering 6 ns typical propagation delay (25°C, 5V), TTL-compatible inputs, and latch-up performance exceeding 250 mA per JESD 17 - used for bus-oriented data routing in industrial control and digital instrumentation systems.

For engineers reviewing the SN74AHCT257BQBR datasheet, SN74AHCT257BQBR pinout, SN74AHCT257BQBR application, or SN74AHCT257BQBR equivalent, key selection criteria include its 16-pin WQFN (BQB) package, shared A/B and OE control logic, 3-state output drive capability (±8 mA), and guaranteed operation across –40°C to +125°C.

Technical Context

The SN74AHCT257BQBR implements four independent 2:1 multiplexers sharing a common data-select (A/B) input 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 logic level of A/B, while OE simultaneously places all outputs in high-impedance state when asserted.

Its balanced CMOS three-state outputs support bidirectional bus interfacing with symmetrical sourcing/sinking capability (IOH = –8 mA, IOL = 8 mA at V_CC = 5 V), and TTL-compatible inputs accept standard 0.8 V/2.0 V thresholds without external level translation - enabling direct connection to legacy TTL logic families.

Key Specifications

Pinout & Package

SN74AHCT257BQBR uses a 16-pin WQFN package (BQB) with 3.6 mm × 2.6 mm body size and exposed thermal pad. The pad may be connected to GND or left floating; it must not connect to any signal or supply voltage.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74AHCT257BQBR, SN74AHCT157PW offers identical functionality in a larger, thermally less efficient package, while 74LVC157AD,118 shifts voltage domain and timing - making SN74AHCT257BQBR the sole choice for compact, robust 5 V bus multiplexing with industrial temperature support.

Availability

SN74AHCT257BQBR is available at Aetrix Electronics and suitable for industrial automation, test equipment, and embedded control systems requiring stable component supply, long-term lifecycle assurance, and RoHS-compliant packaging.

Supply support for SN74AHCT257BQBR 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 experience in high-reliability industrial and automotive-grade components.

The SN74AHCT257BQBR belongs to TI's AHCT logic family - designed specifically for 5 V systems requiring TTL compatibility, low power, and robust noise immunity in harsh electrical environments.

FAQ

What is the maximum capacitive load SN74AHCT257BQBR can drive while meeting datasheet timing specs?

The SN74AHCT257BQBR is characterized for CL = 15 pF and CL = 50 pF loads. All switching characteristics in the datasheet - including t_PHL, t_PLH, and enable/disable times - are guaranteed up to 50 pF. Exceeding this capacitance increases propagation delay nonlinearly and may violate setup/hold margins in high-speed interfaces; TI recommends limiting total node capacitance to ≤50 pF for full spec compliance.

Does SN74AHCT257BQBR support hot insertion or live bus swapping?

No, SN74AHCT257BQBR does not support hot insertion. Its absolute maximum ratings specify VI and VO limits of –0.5 V to 7 V, but the device lacks bus-hold or I^off protection. Applying signal voltages before V_CC is stable risks violating input clamp current limits (±20 mA) and may cause latch-up. Always power V_CC and GND before applying input signals.

Can unused inputs on SN74AHCT257BQBR be left floating?

No, unused inputs on SN74AHCT257BQBR must never be left floating. TTL-compatible CMOS inputs exhibit high impedance and undefined logic states when unconnected, leading to excessive current draw, oscillation, and potential damage. TI mandates termination to V_CC or GND - typically via 10 kΩ pull-up/down resistors - for all unused A/B, 1A–4B, and OE pins.

Is the thermal pad on SN74AHCT257BQBR required to be soldered to ground?

No, the thermal pad on SN74AHCT257BQBR (BQB package) may be connected to GND or left electrically floating. TI explicitly states it must not connect to any signal or supply voltage. Grounding improves thermal dissipation (R_θJB = 75.4°C/W), but floating is acceptable if board-level thermal requirements are met - verified via junction temperature calculation using I_CC, power dissipation, and ambient conditions.

How does the shared A/B input affect channel independence in SN74AHCT257BQBR?

The shared A/B input means all four multiplexer channels select the same source (A or B) simultaneously - they are functionally coupled for data-source selection. However, each channel's inputs (1A/1B through 4A/4B) and outputs (1Y through 4Y) remain electrically isolated. This architecture enables coordinated 4-bit-wide data routing without cross-talk, while minimizing control pin count compared to four independent 2:1 MUX ICs.