onsemi SN74LS126AN

Overview

SN74LS126AN from Texas Instruments is a quad bus buffer with individual 3-state outputs, designed for TTL-compatible data bus isolation and driving in industrial control and legacy computing systems. It features low-power Schottky (LS) logic, 14-pin PDIP packaging, active-low output enable (G), and delivers 24 mA sink current at 0.4 V while consuming only 12 mA typical ICC under full operation.

For engineers reviewing the SN74LS126AN datasheet, pinout, applications, or equivalent options, this device is selected for bidirectional bus buffering where per-channel disable control, high-impedance isolation, and compatibility with 5 V TTL signal levels are required - especially in retro-computing interfaces, test equipment backplanes, and legacy instrumentation subsystems.

Technical Context

The SN74LS126AN implements four independent non-inverting buffers, each with an active-low output enable (G) input that places the Y output in high-impedance state when asserted. Its LS process ensures reduced power consumption versus standard TTL while maintaining compatible voltage thresholds (VIL = 0.8 V, VIH = 2.0 V) and drive strength.

Each channel operates with propagation delays of 9–15 ns (tPLH/tPHL) and enable/disable times of 12–25 ns (tPZH/tPZL) under 5 V/25°C conditions with 45 pF load. The device uses totem-pole output stages with no internal pull-ups, requiring external termination only when driving unterminated lines.

Key Specifications

Pinout & Package

SN74LS126AN is housed in a 14-pin plastic dual in-line package (PDIP-N), 0.300" wide, with standard through-hole mounting and JEDEC MO-015 compliance. Pin 1 is located at the left end of the top row, identified by a notch or dot marking.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS126ADR and SN74LS244N, the SN74LS126AN offers direct through-hole compatibility for legacy repair and bench testing, retains per-channel enable granularity unmatched by octal alternatives, and avoids SMT rework or logic restructuring - making it optimal for field service and small-batch retro-system maintenance.

Availability

SN74LS126AN is available at Aetrix Electronics and suitable for industrial backplane interfacing, retro-computing bus expansion, and legacy instrumentation data acquisition requiring stable component supply and long-term obsolescence mitigation.

Supply support for SN74LS126AN 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 founded in 1930, specializing in analog, embedded processing, and logic solutions with broad industrial and automotive reach.

The SN74LS126AN belongs to TI's legacy 74LS logic family, engineered for reliability and interoperability in 5 V TTL systems - targeting repair, maintenance, and backward-compatible design of industrial controllers and vintage computing hardware.

FAQ

What is the function of the G inputs on the SN74LS126AN?

The G inputs (pins 1, 4, 10, and 13) are active-low output enable controls for each of the four buffers. When a G input is logic low, its corresponding Y output follows the A input; when high, the Y output enters high-impedance state. This allows independent tri-state control per channel - a key differentiator from grouped-enable devices like the SN74LS244N. The SN74LS126AN thus supports fine-grained bus arbitration without additional logic.

Can the SN74LS126AN drive a 50 pF load at 10 MHz reliably?

Yes. With tPLH/tPHL of 9 ns/8 ns typical and tPZH/tPZL of 16 ns/21 ns (at 45 pF), the SN74LS126AN maintains clean edges into 50 pF loads at 10 MHz clock rates. Its 24 mA sink current ensures fast low-to-high transitions even with trace capacitance, and the LS process minimizes shoot-through current. For sustained 10 MHz operation, proper VCC decoupling (0.1 µF ceramic near pin 14) is essential - confirmed in the SN74LS126AN datasheet Figure 2 load circuit.

Is the SN74LS126AN pin-compatible with the SN74LS125AN?

No. While both are quad 3-state buffers in 14-pin PDIP, the SN74LS125AN uses active-high enable (G), whereas the SN74LS126AN uses active-low enable (G). Their pinouts differ: SN74LS125AN assigns G inputs to pins 1, 4, 10, and 13 (same physical locations), but logic polarity reversal means direct substitution would invert enable behavior. The SN74LS126AN requires inverted control signals relative to SN74LS125AN - verified in the SDLS044A datasheet logic diagrams.

What is the maximum junction temperature for continuous operation of the SN74LS126AN?

The SN74LS126AN has a maximum junction temperature (TJ) of 150°C, derived from its absolute maximum rating of 150°C storage temperature and θJA = 80°C/W for the N-package. At 12 mA ICC and 5 V VCC, power dissipation is ~60 mW; with 10°C/W board-level thermal resistance, TJ remains ~70°C at 60°C ambient - well within safe margin. Derating is not required below 70°C ambient per the SN74LS126AN recommended operating conditions.

Does the SN74LS126AN support hot-swap insertion into a live bus?

No. The SN74LS126AN lacks hot-swap protection circuitry such as power-up sequencing, bus-fault detection, or slew-rate limiting. Inserting it into a powered bus risks latch-up or output contention if G inputs float or settle unpredictably during insertion. For hot-swap use, external series resistors (e.g., 100 Ω) and pull-downs on G inputs are mandatory - as documented in TI application note SCBA011 for LS logic bus interfaces. The SN74LS126AN itself does not guarantee safe hot-plug behavior.