Texas Instruments SN74LS125ADR

Overview

SN74LS125ADR from Texas Instruments is a quad 3-state bus buffer with independent channel enable control, designed for TTL-compatible data bus isolation and driving in industrial control and legacy computing systems. It features 12 mA low-level output drive, 1 mA high-level output sink capability, 15 ns typical propagation delay (tPLH/tPHL), and operates from 4.5 V to 5.5 V supply. The device disables outputs when its active-low G input is high, enabling clean bus contention management.

For engineers reviewing the SN74LS125ADR datasheet, SN74LS125ADR pinout, SN74LS125ADR application, or SN74LS125ADR equivalent, key selection criteria include its 14-pin SOIC-D package, guaranteed 3-state off-impedance (>10⁹ Ω), −0.2 mA input leakage at VI = 0.4 V, and compatibility with 5 V TTL logic families in backplane, memory address buffering, and microprocessor peripheral interfacing.

Technical Context

The SN74LS125ADR implements four independent non-inverting buffers, each with a dedicated active-high enable input (G) that forces the output into high-impedance when logic high. Its LS-TTL circuitry uses bipolar transistor design with Schottky clamping to achieve reduced propagation delay and power consumption versus standard TTL.

Each channel's output stage is a totem-pole configuration with no internal pull-up or pull-down resistors-requiring external termination only if needed for signal integrity. The device supports fan-out of 20 LS-TTL loads and maintains valid VOH ≥ 2.4 V and VOL ≤ 0.4 V under full IOL = 12 mA loading across 0°C to 70°C ambient.

Key Specifications

Pinout & Package

SN74LS125ADR is housed in a 14-pin SOIC (Small Outline Integrated Circuit) package per JEDEC MS-012, with 1.27 mm pitch, 8.75 mm × 3.91 mm body dimensions, and 1.75 mm max height. Pin 1 is located at the top-left corner with a molded index notch.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS126ADR, SN74LS125ADR offers native high-enable logic matching most discrete gate-based control schemes; compared with SN74HC125DR, it delivers superior drive strength and timing predictability in legacy 5 V TTL environments, albeit at higher quiescent current.

Availability

SN74LS125ADR is available at Aetrix Electronics and suitable for industrial PLC backplane interfaces, legacy microprocessor address buffering, and automated test fixture bus arbitration requiring stable component supply and long-term obsolescence mitigation.

Supply support for SN74LS125ADR 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 U.S.-based semiconductor company founded in 1930, specializing in analog, embedded processing, and logic ICs with broad industrial, automotive, and aerospace qualification.

The SN74LS125ADR belongs to TI's legacy 74LS logic family, engineered specifically for reliable 5 V TTL bus interfacing in cost-sensitive, thermally constrained, and EMI-prone industrial control systems.

FAQ

What is the maximum operating temperature range for SN74LS125ADR?

The SN74LS125ADR is rated for operation from 0°C to +70°C ambient temperature, consistent with commercial-grade 74LS logic. This range supports deployment in office automation, laboratory instrumentation, and non-extreme industrial enclosures where forced air cooling is available. The device's thermal impedance (θJA = 86°C/W) and 11 mA typical ICC ensure junction temperatures remain within safe limits under normal PCB layout conditions.

Does SN74LS125ADR require external pull-up resistors on its outputs?

No, SN74LS125ADR does not require external pull-up resistors on its outputs. Its totem-pole output stage actively drives both logic high and low states when enabled, delivering VOH ≥ 2.4 V at IOH = –1 mA and VOL ≤ 0.4 V at IOL = 12 mA. Pull-ups are only necessary if the system design mandates weak high-state bias during 3-state disable - which contradicts the intended bus-isolation function of SN74LS125ADR.

Can SN74LS125ADR be used with 3.3 V logic systems?

SN74LS125ADR is not recommended for direct use with 3.3 V logic systems. Its input thresholds (VIH = 2.0 V min, VIL = 0.7 V max) and output levels (VOH ≈ 3.4 V, VOL ≈ 0.25 V at 5 V VCC) are specified for 5 V TTL operation. Interfacing with 3.3 V devices risks overvoltage damage to inputs and violates VOH/VOL compatibility - level-shifting circuitry or a 74LVC125 alternative is required for mixed-voltage designs.

What is the meaning of "3-state" in SN74LS125ADR's description?

"3-state" refers to SN74LS125ADR's ability to place each output in one of three electrical states: logic high, logic low, or high-impedance (Hi-Z). When the G input is high, the output transistors are fully turned off, presenting >10⁹ Ω impedance to the bus - effectively disconnecting the buffer from the line. This enables multiple devices to share a single bus without contention, a fundamental requirement in multiprocessor and peripheral expansion architectures.

How does SN74LS125ADR differ from SN74LS125AN?

SN74LS125ADR and SN74LS125AN share identical electrical specifications and functionality but differ in packaging and packaging format. SN74LS125ADR uses a 14-pin SOIC-D package supplied in tape-and-reel (2500 units/reel), optimized for automated SMT assembly. SN74LS125AN uses a 14-pin PDIP-N package in tube format (25 units/tube), intended for prototyping, through-hole rework, or legacy wave-solder processes. Both operate over 0°C to 70°C and bear the same LS125A top-side marking.