Texas Instruments SN74LS298DR

Overview

SN74LS298DR from Texas Instruments is a quad 2-input multiplexer with latch function, designed for digital data routing and signal selection in TTL-level logic systems. It features four independent 2:1 multiplexers, each with separate data inputs (A/B), common output (Y), and individual strobe (G) and latch enable (LE) controls. It operates at VCC = 5 V, supports 0°C to 70°C ambient temperature, and is used in address/data bus switching and register file selection.

For engineers reviewing the SN74LS298DR datasheet, SN74LS298DR pinout, SN74LS298DR application, or SN74LS298DR equivalent, key considerations include its dual-function strobe/latch control per channel, TTL-compatible input thresholds, propagation delay of 25 ns typical, and compatibility with standard LS-TTL logic families in industrial control and instrumentation designs.

Technical Context

The SN74LS298DR implements four independent 2:1 data selectors, each with active-low strobe (G) enabling output gating and active-high latch enable (LE) controlling transparent vs. latched operation. Each channel's output Y reflects selected input A or B only when G is low and LE is high; when LE transitions low, the last-selected input is held.

It uses bipolar Schottky TTL technology, ensuring compatibility with other LS-series devices. Input clamp diodes provide ESD protection, and outputs drive standard TTL loads with fan-out of 20. The device does not support three-state outputs or internal pull-ups.

Key Specifications

Pinout & Package

SN74LS298DR is packaged in a 16-pin SOIC (Small Outline Integrated Circuit) with 300-mil body width and gull-wing leads. This surface-mount package supports automated PCB assembly and offers improved thermal and mechanical reliability over through-hole PDIP variants.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar quad 2-input multiplexer with latch applications.

Compared with SN74LS298DR, SN74LS399N offers identical functionality in through-hole form but limits modern SMT production, while SN74F299N trades higher speed for greater power consumption and reduced supply margin-neither is pin-compatible with SN74LS298DR's SOIC package.

Availability

SN74LS298DR is available at Aetrix Electronics and suitable for industrial control systems, digital test instrumentation, legacy bus expansion, and embedded instrumentation requiring stable component supply and long-term obsolescence management.

Supply support for SN74LS298DR 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 company headquartered in Dallas, Texas, specializing in analog, embedded processing, and logic technologies since 1930.

The SN74LS298DR belongs to TI's legacy LS-TTL logic family, engineered for robust interoperability in industrial and test equipment where predictable timing, noise immunity, and backward compatibility are essential.

FAQ

What is the primary function of the SN74LS298DR?

The SN74LS298DR is a quad 2-input multiplexer with latch capability, allowing four independent data paths to be selected between two inputs (A or B) and held stable via latch enable. Its core function is hardware-controlled digital signal routing with deterministic timing-critical in bus arbitration, register access, and test instrumentation where LS-TTL compatibility and low propagation delay matter. The SN74LS298DR delivers this in a 16-pin SOIC package optimized for surface-mount manufacturing.

Does the SN74LS298DR support three-state outputs?

No, the SN74LS298DR does not feature three-state outputs. Its outputs are standard push-pull TTL, capable of driving up to 20 LS-TTL loads but lacking high-impedance (Hi-Z) mode. Output enable is managed solely through the active-low strobe (G) pins, which force the output to a defined logic level (not Hi-Z) when inactive. For bus-sharing applications requiring true three-state behavior, designers must add external buffers or select alternatives like the SN74LS257 series.

What is the role of the LE (Latch Enable) pin on the SN74LS298DR?

The LE (Latch Enable) pin on the SN74LS298DR controls whether the output reflects real-time input selection (LE = high) or holds the last selected value (LE = low). When LE transitions from high to low, the currently selected A/B input is captured and maintained at Y regardless of subsequent changes to S or data inputs. This behavior makes the SN74LS298DR suitable for synchronized sampling and glitch-free data capture in systems where timing alignment with a master clock or control strobe is required.

Can the SN74LS298DR operate at 3.3 V?

No, the SN74LS298DR is specified only for 5 V ±0.5 V operation. Its internal bipolar transistor structure and TTL input thresholds require nominal 5 V supply to meet guaranteed timing, noise margin, and output drive specifications. Operating at 3.3 V results in undefined logic levels, excessive propagation delay, and potential failure to recognize valid inputs. For 3.3 V systems, consider LVCMOS or LVTTL-compatible alternatives such as the SN74LVC257, not the SN74LS298DR.

How does the shared select input (pin 15) affect channel independence in the SN74LS298DR?

The shared select input (S, pin 15) means all four channels of the SN74LS298DR must select the same source-either A or B-for their respective outputs. While strobes (G1–G4) and latch enables (internally tied to LE on pin 16) remain independent per channel, the A/B choice is synchronized across all four. This design reduces control wiring but precludes mixed-source routing (e.g., Y1 = A1, Y2 = B2). If per-channel select is needed, designers must use four discrete 2:1 muxes or alternate ICs like the SN74LS157.