onsemi SN74LS125AD

Overview

SN74LS125AD from Texas Instruments is a quad 3-state bus buffer IC with independent channel enable control, designed for TTL-compatible digital bus interfacing in legacy industrial and computing systems. It features low-impedance active outputs (IOH = –1 mA, IOL = 12 mA), high-impedance disabled state, and operates at 4.5–5.5 V over 0°C to 70°C. Its primary role is bidirectional data isolation on shared buses without external pullups.

For engineers reviewing the SN74LS125AD datasheet, pinout, applications, or equivalent options, key selection criteria include per-channel 3-state control logic (active-low enable), LS-family propagation delay (tPLH/tPHL ≤ 15 ns), thermal resistance (θJA = 86°C/W), and SOIC-14 package compatibility with legacy PCB layouts.

Technical Context

The SN74LS125AD implements four independent non-inverting buffers, each with a dedicated active-high output enable (G) input that disables the output to high-impedance when asserted. Its internal TTL/LS circuitry uses bipolar transistor logic with Schottky clamping to achieve improved speed and reduced saturation delay versus standard 74-series devices.

Each channel drives heavily loaded buses directly due to enhanced high-level output drive capability (VOH ≥ 2.4 V at IOH = –1 mA), eliminating need for external pullup resistors. The device complies with JEDEC MS-012AB for SOIC-D package mechanical dimensions and reflow profile (MSL Level-1, 260°C peak).

Key Specifications

Pinout & Package

SN74LS125AD is housed in a 14-pin Small Outline Integrated Circuit (SOIC) package per JEDEC MS-012AB, with 1.27 mm pitch, 8.75 mm × 3.91 mm body, and 1.75 mm max height.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS125AD, SN74LS125ADR offers modern packaging and full production support, while SN74LS125AN provides mechanical compatibility with older through-hole systems-both retain identical timing, drive, and logic functionality for drop-in replacement in validated designs.

Availability

SN74LS125AD is available at Aetrix Electronics and suitable for microprocessor bus interface, legacy industrial controller, test equipment signal routing, and computer terminal logic applications requiring stable component supply and long-term obsolescence management.

Supply support for SN74LS125AD 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 for industrial, automotive, and communications markets.

The SN74LS125A family was developed in the early 1980s to provide robust, low-power bus buffering for TTL-based computing and control systems-emphasizing reliability, noise immunity, and compatibility with established 5 V infrastructure.

FAQ

What is the function of the G input on SN74LS125AD?

The G input on SN74LS125AD is an active-HIGH output enable control for each of the four independent buffer channels. When G is logic HIGH, the corresponding Y output enters a high-impedance (3-state) condition, electrically disconnecting it from the bus. When G is logic LOW, the Y output follows the A input with non-inverting logic. This enables selective bus arbitration without contention. SN74LS125AD uses this per-channel control to support flexible data routing in multi-peripheral systems.

Can SN74LS125AD drive a 50 pF load at 10 MHz?

Yes, SN74LS125AD can reliably drive a 50 pF capacitive load at 10 MHz. Its specified switching characteristics (tPLH/tPHL ≤ 15 ns at CL = 45 pF, RL = 667 Ω) indicate sufficient bandwidth for this requirement, with measured propagation delay well below the 100 ns period of a 10 MHz signal. SN74LS125AD maintains VOH ≥ 2.4 V and VOL ≤ 0.4 V under these conditions, ensuring TTL logic margin. Layout best practices (short traces, local decoupling) are recommended.

Is SN74LS125AD RoHS compliant?

SN74LS125AD itself is marked as obsolete in TI's packaging documentation and lacks RoHS certification status. However, its direct replacement SN74LS125ADR is RoHS compliant with NIPDAU lead finish and MSL Level-1 rating. For new designs, Aetrix recommends SN74LS125ADR to meet environmental compliance requirements. SN74LS125AD may still be sourced for legacy repair, but its RoHS status is not documented by Texas Instruments.

What is the maximum output short-circuit duration allowed for SN74LS125AD?

The maximum safe output short-circuit duration for SN74LS125AD is one second, as specified in Note 4 of the datasheet. During short-circuit events, output current (IOS) reaches –40 mA (max), and prolonged exposure beyond one second risks thermal damage or parametric shift. SN74LS125AD includes internal current limiting but is not designed for continuous short-circuit operation. System-level protection (e.g., current-limiting resistors or fuses) is advised for high-reliability applications.

How does SN74LS125AD differ from SN74LS126A?

SN74LS125AD and SN74LS126A are complementary 3-state buffer variants: SN74LS125AD uses active-HIGH enable (G HIGH disables output), while SN74LS126A uses active-LOW enable (G LOW disables output). Their electrical specs are nearly identical (same VCC, IOL, VOH/VOL), but control logic polarity differs. SN74LS125AD is optimized for systems where disable signals are asserted high (e.g., tied to microcontroller GPIOs), whereas SN74LS126A suits active-low reset or chip-select architectures.