Texas Instruments SN74AHCT126BQAR

Overview

SN74AHCT126BQAR from Texas Instruments is a quadruple 3-state bus buffer gate IC with TTL-compatible inputs, designed for bidirectional data isolation and level translation in 5-V digital systems. It features four independent noninverting buffers (1A→1Y, 2A→2Y, 3A→3Y, 4A→4Y), each controlled by its own output-enable input (1OE–4OE), supports 8 mA output drive, operates from 4.5 V to 5.5 V, and delivers propagation delays as low as 1 ns at 25°C - enabling use in high-speed PC and server board interconnects.

For engineers reviewing the SN74AHCT126BQAR datasheet, SN74AHCT126BQAR pinout, SN74AHCT126BQAR application, or SN74AHCT126BQAR equivalent, key selection criteria include its WQFN-14 (BQA) thermal performance (RθJA = 88.3°C/W), 3-state output timing (tPLZ/tPHZ ≤ 8.5 ns), latch-up immunity (>250 mA), and compatibility with 3.3-V logic driving 5-V buses.

Technical Context

The SN74AHCT126BQAR implements four independent CMOS buffer stages with TTL-voltage-compatible input thresholds (VIH = 2 V, VIL = 0.8 V), enabling reliable up-translation from 3.3-V logic domains to 5-V buses. Its 3-state outputs are fully decoupled per channel, allowing selective bus arbitration without contention.

Each buffer operates under strict recommended conditions: VCC = 4.5–5.5 V, TA = –40°C to 125°C, with input transition rates limited to 20 ns/V to suppress ringing. The device uses standard CMOS fabrication with enhanced ESD protection (2000-V HBM, 200-V MM) and exceeds JESD 17 latch-up requirements.

Key Specifications

Pinout & Package

SN74AHCT126BQAR is housed in a 14-pin WQFN package (BQA) with exposed thermal pad, measuring 3.5 mm × 3.5 mm × 0.8 mm. The package supports fine-pitch routing and provides superior thermal performance versus SOIC or TSSOP alternatives.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar bus buffer applications.

Compared with SN74AHCT126BQAR, SN74AHCT125BQAR offers identical electrical behavior except polarity, making it a drop-in replacement where inversion is acceptable; SN74LVC126APWR trades voltage flexibility and TTL compatibility for higher speed and lower voltage operation, requiring full system voltage redesign.

Availability

SN74AHCT126BQAR is available at Aetrix Electronics and suitable for server motherboard design, industrial PLC backplane interconnects, and medical imaging subsystems requiring stable component supply across extended product lifecycles.

Supply support for SN74AHCT126BQAR 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 over 90 years of innovation in high-reliability electronic components.

SN74AHCT126BQAR belongs to TI's AHCT logic family, engineered for robust 5-V bus interfacing with TTL compatibility, industrial temperature range, and enhanced ESD/latch-up resilience - targeting mission-critical computing and control infrastructure.

FAQ

What is the maximum operating temperature for SN74AHCT126BQAR?

The SN74AHCT126BQAR is rated for continuous operation from –40°C to +125°C ambient temperature. This specification is validated per JEDEC JESD78 and confirmed in TI's production test flow for the BQA package variant. Thermal derating begins above 125°C, and junction temperature must remain below 150°C under all operating conditions. The WQFN package's RθJA of 88.3°C/W enables this rating with appropriate PCB copper area.

Does SN74AHCT126BQAR support 3.3-V input logic levels?

Yes, SN74AHCT126BQAR explicitly supports 3.3-V input logic levels due to its TTL-compatible input thresholds: VIH = 2.0 V (minimum) and VIL = 0.8 V (maximum). A 3.3-V CMOS high-level signal (≥2.4 V) exceeds VIH, and a low-level signal (≤0.4 V) remains below VIL - ensuring reliable detection without external biasing. This makes SN74AHCT126BQAR ideal for up-translation interfaces.

Can SN74AHCT126BQAR drive standard 5-V TTL loads?

Yes, SN74AHCT126BQAR can directly drive standard 5-V TTL loads. Its output drive capability is ±8 mA at VCC = 4.5 V, with VOH ≥ 3.8 V and VOL ≤ 0.44 V under those conditions - satisfying TTL input requirements (VIH ≥ 2.0 V, VIL ≤ 0.8 V) while sourcing/sinking sufficient current for fan-out of 10 LS-TTL loads. No series termination or pull-ups are required.

Is the thermal pad on SN74AHCT126BQAR required to be connected?

Yes, the exposed thermal pad on SN74AHCT126BQAR must be soldered to a PCB thermal land to achieve the published RθJA of 88.3°C/W. Leaving it unconnected degrades thermal resistance by >40%, risking junction temperatures exceeding 150°C under moderate load. TI recommends a 3.5 mm × 3.5 mm copper pad with 4–9 thermal vias to an internal ground plane for optimal performance.

What happens to outputs during power-up or power-down of SN74AHCT126BQAR?

During power-up or power-down, SN74AHCT126BQAR outputs enter a high-impedance state only if OE pins are held low - but default behavior is undefined. TI recommends tying each OE pin to GND via a pull-down resistor (≤10 kΩ) to ensure predictable 3-state behavior at all VCC levels. This prevents bus contention and back-driving of upstream logic during supply transitions.