Texas Instruments SN74F126D

Overview

SN74F126D from Texas Instruments is a quadruple bus buffer gate with 3-state outputs, designed for bidirectional data bus isolation and memory address register buffering in TTL-compatible digital systems. It operates from 4.5 V to 5.5 V, delivers max propagation delay of 6.5 ns at 5 V, and supports independent output-enable control per channel - enabling selective bus driving in multi-master architectures.

For engineers reviewing the SN74F126D datasheet, SN74F126D pinout, SN74F126D application, or SN74F126D equivalent, key selection criteria include 3-state output timing (tPZH/tPLZ ≤ 8.5 ns), ±64 mA low-level drive capability, thermal resistance (θJA = 86°C/W), and SOIC-14 package compatibility with legacy F-series TTL logic families.

Technical Context

The SN74F126D implements four independent noninverting buffers, each with dedicated active-high output-enable (OE) control. Each channel transitions to high-impedance state when OE is low, decoupling the output from the bus without requiring external pull-up resistors.

It adheres to standard F-series TTL electrical characteristics: VIH = 2 V min, VIL = 0.8 V max, IOL = 64 mA, IOH = –15 mA, and supports operation across 0°C to 70°C ambient. Input clamp current (–18 mA) and absolute maximum ratings (e.g., VI = –1.2 V to 7 V) ensure robustness against transient overvoltage and ESD-induced latch-up during hot-swap or power sequencing.

Key Specifications

Pinout & Package

SN74F126D is housed in a 14-pin SOIC (D) package with 1.27 mm pitch, 8.75 mm × 3.9 mm body, and 1.75 mm max height - compatible with standard surface-mount reflow profiles (MSL Level-1, 260°C peak).

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS126N and SN74ACT126D, the SN74F126D occupies a mid-tier position: faster and more drive-capable than LS, yet simpler to interface than ACT due to TTL-compatible inputs - making it optimal for upgrading legacy F-series systems without redesigning driver stages.

Availability

SN74F126D is available at Aetrix Electronics and suitable for memory subsystem design, microprocessor bus expansion, and industrial I/O interface applications requiring stable component supply and long-term obsolescence management.

Supply support for SN74F126D 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 TTL and advanced logic families.

The SN74F126D belongs to TI's 74F fast TTL logic product line, engineered for high-speed digital systems requiring deterministic timing, robust noise immunity, and direct compatibility with legacy 5-V logic architectures.

FAQ

What is the recommended power-up sequence for SN74F126D to avoid bus contention?

TI recommends tying all OE pins to GND through a pulldown resistor (value determined by driver sourcing capability) to ensure outputs remain in high-impedance state until system initialization completes. This prevents unintended bus driving during VCC ramp-up. The SN74F126D datasheet specifies this as mandatory for reliable power sequencing - especially critical in multi-buffered bus systems where SN74F126D outputs may connect to shared lines.

Can SN74F126D drive standard TTL loads directly without external components?

Yes. The SN74F126D provides 64 mA low-level output current (IOL) and –15 mA high-level output current (IOH), meeting or exceeding standard TTL loading requirements (16 mA sink per input). Its VOH ≥ 2.4 V and VOL ≤ 0.55 V at full load ensure noise margins exceed 0.4 V - enabling direct connection to 74F, 74LS, and 74ALS inputs without series resistors or level shifters. This capability is explicitly verified in the SN74F126D electrical characteristics table.

Is SN74F126D pin-compatible with other 74xx126 variants like SN74LS126 or SN74HC126?

No. While SN74F126D shares the same 14-pin SOIC (D) package and functional pinout (1OE–1A–1Y–2OE–2A–2Y–GND–VCC–4OE–4A–4Y–3OE–3A–3Y) with SN74LS126N and SN74HC126D, voltage thresholds and timing differ significantly. SN74F126D requires 4.5–5.5 V operation and TTL input levels; SN74HC126 operates from 2–6 V with CMOS thresholds. Direct substitution without circuit review risks logic failure or excessive power draw - the SN74F126D is not a drop-in replacement outside F-family systems.

What is the maximum capacitive load SN74F126D can drive while maintaining specified tpd?

The SN74F126D's switching characteristics are characterized at CL = 50 pF, which represents the maximum load for guaranteed 6.5 ns tpd (at 5 V). Driving heavier loads increases propagation delay nonlinearly - e.g., at 100 pF, tpd exceeds 10 ns. For reliable timing closure in high-speed buses, keep total trace + input capacitance ≤ 50 pF per SN74F126D output, or add series termination if longer traces are unavoidable. This limit is defined in the SN74F126D switching characteristics table.

Does SN74F126D support hot-swap or live-insertion in backplane applications?

The SN74F126D is not rated for hot-swap operation. Its absolute maximum ratings specify VI ≤ –1.2 V and VO ≤ 5.5 V in disabled state, but no built-in current limiting or slew-rate control exists for insertion into a live bus. TI advises using external series resistors or dedicated hot-swap controllers when inserting SN74F126D-equipped modules into powered backplanes - particularly because the SN74F126D lacks bus-hold or power-off protection features found in newer logic families.