DM74S240N

Overview

The DM74S240N is an octal 3-STATE buffer and line driver manufactured by onsemi (formerly Fairchild Semiconductor). It features inverted outputs and operates within a supply voltage range of 4.75V to 5.25V. The device provides high fanout with typical sink currents of 64mA and source currents of -15mA. Designed for improved noise rejection, it includes 400mV hysteresis at the low current PNP data inputs. Typical propagation delay times are 4.5ns for inverting operations. It is housed in a 20-Lead Plastic Dual-In-Line Package (PDIP) suitable for through-hole mounting.

Feature Summary

• Features 3-STATE outputs that drive bus lines directly
• Utilizes PNP inputs to reduce DC loading on bus lines
• Includes hysteresis at data inputs to improve noise margins
• Capable of driving terminated lines down to 133Ω

Applications

• Memory-address drivers
• Clock drivers
• Bus-oriented transmitters/receivers

Procurement Notes

Verify component authenticity as this part may be obsolete or superseded by newer equivalents. Confirm package dimensions match the N20A specification. Check datasheet revisions for any electrical characteristic updates. Ensure environmental compliance requirements align with project specifications before procurement.

Selection Notes

Select this component for applications requiring high-speed signal buffering with noise immunity. The PNP input structure offers reduced loading compared to standard TTL. Verify that the required propagation delay and output drive strength meet system timing constraints. Consider thermal dissipation requirements under maximum load conditions.

Part Context

This device belongs to the 74S series logic family, known for Schottky-clamped transistor technology providing faster switching speeds than standard TTL. The octal configuration allows for efficient handling of wide data buses. It serves as a critical interface component in digital systems requiring reliable signal transmission across bus architectures.

Replacement Considerations

SN74AS240AN Texas Instruments

FAQ

What is the purpose of the hysteresis feature in this buffer?

The 400mV hysteresis at the data inputs improves noise margins, allowing the device to reject noise effectively when driving terminated lines.

How does the PNP input structure benefit the circuit?

The PNP inputs reduce DC loading on bus lines, which helps maintain signal integrity and improves overall performance in bus-oriented applications.