Texas Instruments SN74LS109ADR

Overview

SN74LS109ADR from Texas Instruments is a dual J-K positive-edge-triggered flip-flop with individual set and reset inputs, designed for synchronous logic control in TTL-based digital systems. It operates from 4.75 V to 5.25 V, supports 0°C to 70°C ambient temperature, features 16-pin SOIC packaging, and delivers typical propagation delay of 20 ns (clock to Q) at V_CC = 5 V.

For engineers reviewing the SN74LS109ADR datasheet, SN74LS109ADR pinout, SN74LS109ADR application, or SN74LS109ADR equivalent, key selection criteria include edge-triggering behavior, independent asynchronous set/reset per section, TTL-compatible input thresholds, and SOIC-16 thermal and layout compatibility in legacy industrial control and test equipment designs.

Technical Context

The SN74LS109ADR implements two independent J-K flip-flops, each with separate J, K, clock, set (SD), and reset (RD) terminals. Its positive-edge-triggered clock input ensures state updates only on rising transitions, while asynchronous SD and RD inputs override clock timing to force Q high or low regardless of clock phase.

Designed for TTL logic families, it interfaces directly with 74LS, 74S, and 74F series devices without level-shifting. Input clamp diodes and internal current-limiting resistors enable robust noise immunity and bus-driving capability up to 20 mA sink per output.

Key Specifications

Pinout & Package

SN74LS109ADR uses a 16-pin Small Outline Integrated Circuit (SOIC) package with 1.27 mm pitch, 7.5 mm body width, and gull-wing leads. Pin 1 is located in quadrant Q1 per TI tape-and-reel specification.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual J-K flip-flop applications.

Compared with SN74LS109ADR, SN74LS112ADR shifts timing alignment to falling clock edges-critical for systems with fixed clock polarity-while SN74LS76N sacrifices surface-mount compatibility and RoHS compliance for through-hole availability, limiting use to non-production or maintenance contexts.

Availability

SN74LS109ADR is available at Aetrix Electronics and suitable for industrial control panels, legacy test instrumentation, and avionics LRU repair programs requiring stable component supply and long-term obsolescence mitigation.

Supply support for SN74LS109ADR 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 and aerospace qualification.

The SN74LS109ADR belongs to TI's legacy 74LS logic family, engineered for reliability in commercial-grade digital control systems where predictable timing, noise margin, and backward compatibility are essential.

FAQ

What is the maximum operating frequency supported by the SN74LS109ADR?

The SN74LS109ADR has a typical propagation delay of 20 ns from clock to Q output at V_CC = 5 V, supporting a maximum reliable clock frequency of approximately 25 MHz under standard load conditions. This limit assumes proper decoupling, controlled trace impedance, and minimal capacitive loading on outputs. Higher frequencies may cause setup/hold violations or metastability, especially with marginal input rise times.

Does the SN74LS109ADR support hot-swapping or live insertion?

No, the SN74LS109ADR does not support hot-swapping. Its TTL input structure lacks bus-hold or I²C-style clamping, and powering V_CC while signals are active can cause latch-up or excessive current draw. Always power down the board before inserting or removing the SN74LS109ADR to prevent damage to the IC or surrounding circuitry.

Can the SN74LS109ADR replace the obsolete SN74LS109AD in existing designs?

Yes, the SN74LS109ADR is a direct RoHS-compliant replacement for the obsolete SN74LS109AD, sharing identical SOIC-16 package, pinout, DC/AC specifications, and marking "LS109A". No PCB or firmware changes are required-only verification that the new MSL-1 rating aligns with reflow profile settings during assembly.

What is the purpose of the separate SD and RD inputs on each section of the SN74LS109ADR?

The separate SD (set) and RD (reset) inputs on each section of the SN74LS109ADR provide asynchronous control to force Q high or low regardless of clock state-enabling immediate initialization, fault recovery, or emergency shutdown. These active-low inputs dominate over J/K logic and operate independently per section, allowing selective reset without disturbing the other flip-flop's state.

Is the SN74LS109ADR compatible with 3.3 V logic systems?

No, the SN74LS109ADR is strictly a 5 V TTL device with V_CC range 4.75 V–5.25 V and input thresholds defined for 5 V operation (V_IH ≥ 2.0 V, V_IL ≤ 0.8 V). Driving its inputs from 3.3 V logic may result in undefined states or increased static current. Level-shifting circuitry is required for interfacing with 3.3 V systems.