Texas Instruments SN74AHCT126DBR

Overview

SN74AHCT126DBR from Texas Instruments is a quadruple bus buffer gate with independent 3-state outputs, designed for bidirectional bus interfacing in 5-V digital systems. It features TTL-compatible inputs (VIH = 2 V, VIL = 0.8 V), ±8 mA output drive, propagation delay of 1–7 ns (CL = 15–50 pF), and operates from –40°C to +125°C. It enables level translation from 3.3-V logic to 5-V buses in PC and server I/O expansion.

For engineers reviewing the SN74AHCT126DBR datasheet, SN74AHCT126DBR pinout, SN74AHCT126DBR application, or SN74AHCT126DBR equivalent, key selection criteria include 3-state output control timing (tPZH/tPLZ ≤ 6.5 ns), input overvoltage tolerance up to 5.5 V, thermal resistance (RθJA = 107.1°C/W for SSOP), and compatibility with legacy TTL signal levels in mixed-voltage board designs.

Technical Context

The SN74AHCT126DBR implements four independent noninverting buffers, each with dedicated output-enable (OE) control. Each channel transitions between active drive (A → Y) and high-impedance state based solely on its OE input-no internal bus arbitration or direction control logic is present.

Its CMOS design with TTL-input thresholds enables seamless interfacing between 3.3-V microcontrollers and 5-V peripheral buses. Slow edge rates (Δt/Δv = 20 ns/V) reduce output ringing and EMI, while latch-up immunity (>250 mA per JESD 17) supports robust operation in noisy industrial environments.

Key Specifications

Pinout & Package

SN74AHCT126DBR uses a 14-pin SSOP (Shrink Small Outline Package) with 0.65 mm lead pitch, 5.3 mm × 6.2 mm body size, and exposed thermal pad not present (BQA package only has thermal pad).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LVC126A and 74ACT126, the SN74AHCT126DBR uniquely balances 5-V compatibility, TTL input compatibility, and certified 2000-V HBM protection - making it the preferred choice for upgrading legacy 5-V systems with modern reliability requirements.

Availability

SN74AHCT126DBR is available at Aetrix Electronics and suitable for server backplanes, PC I/O expansion, and industrial HMI designs requiring stable component supply, extended-temperature operation, and proven ESD resilience.

Supply support for SN74AHCT126DBR 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 connectivity technologies, with decades of experience in logic IC design and industrial-grade qualification.

The SN74AHCT126DBR belongs to TI's AHCT logic family, engineered for interoperability between TTL and CMOS systems in commercial-temperature 5-V applications - emphasizing robustness, predictable timing, and ease of integration.

FAQ

What is the maximum input voltage allowed on SN74AHCT126DBR pins?

The SN74AHCT126DBR inputs are overvoltage tolerant up to 5.5 V, regardless of VCC level. This allows safe operation during power sequencing mismatches or transient coupling, and supports direct connection to 5-V TTL sources even when VCC is at nominal 5.0 V. The absolute maximum rating is 5.5 V - exceeding this risks permanent damage.

Does SN74AHCT126DBR support hot-swap applications?

Yes, SN74AHCT126DBR supports hot-swap use cases through its independent 3-state outputs. By asserting OE low before card insertion, outputs enter high-impedance mode, preventing backdrive into live backplane rails. Its 2000-V HBM ESD rating and latch-up immunity (>250 mA) further enhance reliability during plug-in events.

Can SN74AHCT126DBR translate 3.3-V logic to 5-V bus levels?

Yes, SN74AHCT126DBR is explicitly designed for 3.3-V-to-5-V up-translation. Its TTL-compatible inputs (VIH = 2.0 V, VIL = 0.8 V) reliably recognize 3.3-V logic highs and lows, while its 5-V CMOS outputs drive standard 5-V bus loads with ±8 mA drive strength - eliminating need for external level shifters in many cases.

What is the thermal resistance of SN74AHCT126DBR in its SSOP package?

The SN74AHCT126DBR in SSOP (DB) package has RθJA = 107.1°C/W, RθJC(top) = 59.6°C/W, and RθJB = 54.4°C/W. These values reflect its thermal performance on standard FR-4 PCBs with typical copper pour; actual junction temperature rise depends on airflow, board stack-up, and local copper area around the device.

How should unused inputs be handled on SN74AHCT126DBR?

All unused inputs on SN74AHCT126DBR must be tied to either VCC or GND - never left floating. Floating inputs cause undefined output states, increased ICC current, and potential oscillation. For OE pins, tie to GND to disable that buffer; for A inputs, tie to GND or VCC depending on desired default output state (low or high).