Texas Instruments SN74HC126D

Overview

SN74HC126D from Texas Instruments is a quadruple 3-state buffer IC used for digital signal enabling and bus isolation in CMOS logic systems. It features four independent non-inverting buffers (Y = A), operates from 2 V to 6 V, supports –40°C to +85°C ambient temperature, delivers ≤31 ns propagation delay at 6 V with 50 pF load, and drives up to 10 LSTTL loads - commonly deployed in bidirectional data bus control and I/O expansion circuits.

For engineers reviewing the SN74HC126D datasheet, SN74HC126D pinout, SN74HC126D application, or SN74HC126D equivalent, this page provides verified functional identity, SOIC-14 package mapping, 3-state timing parameters, thermal resistance (R_θJA = 133.6°C/W), and validated alternative options for bus interface design.

Technical Context

The SN74HC126D implements four identical CMOS buffer channels, each with separate input (A), output enable (OE), and 3-state output (Y) terminals. Its Boolean function Y = A is implemented using balanced CMOS output stages capable of sourcing and sinking up to ±7.8 mA at 6 V while maintaining VOH ≥ 5.34 V and VOL ≤ 0.33 V under load.

Each channel operates independently: OE low places Y in high-impedance state (IOZ ≤ ±0.5 µA); OE high enables pass-through buffering with propagation delay t_pd as low as 11 ns (6 V, CL = 50 pF). Input structure includes clamp diodes and standard CMOS impedance (Ci ≤ 10 pF), requiring fast edge rates (t_t ≤ 400 ns at 6 V) to avoid shoot-through current.

Key Specifications

Pinout & Package

SN74HC126D is housed in a 14-pin SOIC (Small Outline Integrated Circuit) package with nominal body dimensions of 8.70 mm × 3.90 mm and standard JEDEC MS-012AC footprint. The package is RoHS-compliant, lead-finish NIPDAU/SN, MSL Level-1, and rated for reflow up to 260°C.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 3-state buffer applications.

Compared with SN74HC126D, SN74HCT126D offers improved noise margin in 5 V TTL environments but higher static power, while 74LVC126AD,118 delivers superior speed and density at 3.3 V but lacks 6 V operation - making SN74HC126D the optimal choice for wide-supply-flexibility industrial bus isolation.

Availability

SN74HC126D is available at Aetrix Electronics and suitable for industrial bus isolation, microcontroller I/O expansion, test equipment signal routing, and legacy system interface adapter applications requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for SN74HC126D 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 heritage in high-reliability logic families including the 74HC series.

The SN74HC126D belongs to TI's industry-standard 74HC logic family, designed specifically for robust, low-power, wide-voltage-range digital interfacing in industrial, automotive, and communications equipment.

FAQ

What is the maximum capacitive load the SN74HC126D can drive while meeting datasheet timing specifications?

The SN74HC126D is characterized for CL ≤ 50 pF in switching specifications, with typical performance maintained up to 70 pF in layout practice. Driving >70 pF risks exceeding t_pd, t_en, and t_dis limits - especially at 2 V supply. For larger loads, add a series resistor to limit peak output current per Absolute Maximum Ratings (±35 mA).

Can unused inputs on the SN74HC126D be left floating?

No - unused inputs on the SN74HC126D must be terminated to VCC or GND. Floating CMOS inputs cause undefined logic states, increased ICC, and potential oscillation due to noise coupling. A 10-kΩ pull-up or pull-down resistor is recommended for unused OE or A pins to ensure stable operation and prevent shoot-through current.

Does the SN74HC126D support 3.3 V operation with guaranteed timing performance?

Yes - the SN74HC126D is fully specified at 3.3 V (VCC = 3.3 V falls within 2–6 V range). At 3.3 V, t_pd is ≤ 20 ns (CL = 50 pF), VOH ≥ 3.15 V, and VOL ≤ 0.33 V, satisfying standard 3.3 V LVTTL and LVCMOS interface requirements without derating.

What is the thermal resistance (RθJA) of the SN74HC126D in its SOIC-14 package?

The SN74HC126D in SOIC-14 (D package) has R_θJA = 133.6°C/W, measured under standard JEDEC JESD51-2 conditions (single-layer board, 1 in² copper pad). This value assumes no internal copper planes; actual board-level thermal performance improves significantly with proper PCB copper pour and thermal vias beneath the package.

How does the SN74HC126D behave when multiple channels share a common bus line?

When multiple SN74HC126D outputs connect to one bus line, only one channel's OE should be active (low) at a time. Simultaneous OE activation causes bus contention and violates Absolute Maximum Ratings (IO ≤ ±35 mA per output). The 3-state architecture enables safe wired-OR or shared-bus topologies only when OE signals are mutually exclusive via external control logic.