Texas Instruments SN74LS298D

Overview

SN74LS298D from Texas Instruments is a quad 2-input multiplexer with common strobe and complementary outputs, implemented in bipolar LS-TTL logic. It features 16-pin PDIP packaging, operates over 0°C to 70°C, supports 5V nominal supply, and delivers typical propagation delay of 15 ns at V_CC = 5V. It is used in digital data routing, function generator control, and address/data bus selection in legacy microprocessor systems.

For engineers reviewing the SN74LS298D datasheet, SN74LS298D pinout, SN74LS298D application, or SN74LS298D equivalent, key selection considerations include strobe-controlled data gating, complementary output drive capability, TTL-compatible input thresholds, and compatibility with standard LS-TTL fan-out and timing budgets.

Technical Context

The SN74LS298D integrates four independent 2:1 multiplexers sharing a single active-low strobe (G̅) that enables all channels simultaneously. Each channel accepts two data inputs (A/B), selects one via select line (S), and drives both true and inverted outputs (Y/Y̅).

Its LS-TTL design ensures compatibility with 74LS family logic levels and loading, with guaranteed high-level output voltage ≥2.7V at I_OH = –0.4 mA and low-level output voltage ≤0.5V at I_OL = 8 mA. Propagation delays are specified under standard load conditions (C_L = 15 pF, R_L = 1 kΩ).

Key Specifications

Pinout & Package

SN74LS298D is supplied in a 16-pin plastic dual in-line package (PDIP), with 0.3-inch body width and standard through-hole mounting footprint.

Key Features

Applications

Equivalent & Alternatives

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

Compared with SN74LS157N and SN74LS158N, the SN74LS298D uniquely provides true/inverted outputs per channel in the same 16-pin PDIP package-enabling direct interface to both polarities of downstream logic without added gates or layout changes.

Availability

SN74LS298D is available at Aetrix Electronics and suitable for legacy system repair, educational lab equipment, industrial controller refurbishment, and aerospace obsolescence mitigation requiring stable component supply and long-term traceability.

Supply support for SN74LS298D 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 ICs, embedded processors, and logic devices with broad industrial, automotive, and consumer reach.

The SN74LS298D belongs to TI's legacy 74LS logic product line, engineered for reliability and interoperability in fixed-function digital systems where predictable timing, robust noise immunity, and through-hole serviceability remain critical.

FAQ

What is the function of the strobe pin (G̅) on the SN74LS298D?

The strobe pin (G̅, Pin 1) is an active-low enable that controls all four multiplexer channels simultaneously. When G̅ is high, all outputs (Y and Y̅) enter high-impedance state regardless of select or input states. Only when G̅ is low do the channels respond to S and A/B inputs. This allows synchronized gating of data paths in timing-critical systems using the SN74LS298D.

Does the SN74LS298D support 3.3V operation?

No, the SN74LS298D is strictly a 5V-only device. Its internal bipolar transistor structure and LS-TTL input thresholds require V_CC between 4.75 V and 5.25 V. Operation at 3.3V will result in undefined logic states, excessive propagation delay, or failure to recognize valid high-level inputs. For 3.3V systems, consider modern CMOS alternatives-not the SN74LS298D.

How many independent data channels does the SN74LS298D provide?

The SN74LS298D provides four independent 2:1 multiplexer channels. Each channel has dedicated A and B inputs, a shared select line (S), and separate true (Y) and inverted (Y̅) outputs. All channels share the same strobe (G̅) and supply (V_CC/GND) connections, enabling coordinated operation while maintaining electrical isolation between data paths in the SN74LS298D.

Can the SN74LS298D replace the SN74LS157N in an existing design?

The SN74LS298D is pin-compatible with the SN74LS157N for all shared pins (inputs, outputs, strobe, select, supply), but adds Y̅ outputs on Pins 5, 9, 12, and 14-previously no-connect on SN74LS157N. If those pins are unconnected or terminated, SN74LS298D can serve as a functional upgrade. However, existing traces tied to those pins must be verified before substitution in the SN74LS298D.

What is the maximum recommended capacitive load for SN74LS298D outputs?

TI specifies a maximum load capacitance of 15 pF for guaranteed timing performance (t_PD, t_PLH, t_PHL) in the SN74LS298D datasheet. Exceeding this value increases propagation delay nonlinearly and may cause marginal setup/hold violations in high-speed synchronous designs. For heavier loads, buffer stages or lower-capacitance routing practices are required to maintain reliable operation of the SN74LS298D.