SN74HCT138NSR

Overview

The SN74HCT138NSR is a 3-line to 8-line decoder/demultiplexer from the Texas Instruments SNx4HCT138 family. It operates within a supply voltage range of 4.5 V to 5.5 V and features TTL-compatible inputs with low input current (1 µA max). The device provides active-low outputs capable of driving up to 10 LSTTL loads, with ±4-mA output drive at 5 V. Typical propagation delay is 17 ns at 5.5 V. It incorporates three enable inputs (one active-high G1, two active-low G2A/G2B) to simplify cascading. Packaged in a 16-pin Small Outline Package (SOP), it supports surface-mount assembly.

Feature Summary

• TTL-voltage compatible inputs for direct interfacing with standard logic families
• Three enable inputs allow flexible expansion and demultiplexing applications
• Active-low outputs designed for high-performance memory decoding systems

Applications

• High-speed memory address decoding
• Data routing and transmission systems
• Demultiplexing signal distribution

Procurement Notes

Verify the package designation matches the SOP-16 form factor required for your PCB layout. Confirm the suffix 'SR' indicates tape-and-reel packaging suitable for automated assembly processes. Ensure the operating environment stays within the specified -40°C to +85°C temperature range. Check that the 4.5V to 5.5V supply voltage aligns with your system power rails before finalizing procurement.

Selection Notes

Select this component when TTL-level compatibility is required alongside CMOS low-power characteristics. The HCT series ensures noise margins compatible with TTL inputs while maintaining lower static power consumption than standard LS logic. Consider the three-enable architecture if system expansion or complex gating logic is needed without additional external gates.

Part Context

This part belongs to the SNx4HCT138 family of 3-to-8 line decoders. It is the commercial-grade version of the SN54HCT138, differing primarily in the operating temperature range (-40°C to +85°C versus -55°C to +125°C). The NS package variant specifically denotes the small outline package configuration.

Replacement Considerations

SN74HCT138DR

FAQ

How many enable inputs does the SN74HCT138NSR have?

It has three enable inputs: one active-high (G1) and two active-low (G2A and G2B).

What is the typical propagation delay time?

The typical propagation delay time is 17 ns.