SN74HCT138DR

Overview

The SN74HCT138DR is a 3-line to 8-line decoder/demultiplexer manufactured by Texas Instruments in the 74HCT logic family. It operates within a supply voltage range of 4.5 V to 5.5 V and features three enable inputs for simplified cascading. The device utilizes a SOIC-16 surface-mount package with dimensions of 9.90 mm x 3.90 mm. It supports an operating temperature range from -40°C to +85°C and includes TTL-compatible inputs.

Feature Summary

• Designed for high-performance memory decoding and data routing applications requiring short propagation delays
• Incorporates two active-low and one active-high enable inputs to simplify expansion without external gates
• Features TTL-voltage compatible inputs and low input current characteristics

Applications

• High-speed memory systems
• Data transmission systems
• Cascaded decoder configurations

Procurement Notes

Verify that the specific orderable part number matches the required package type, as the SN74HCT138 series is available in multiple form factors including PDIP, TSSOP, and SOP. Confirm the suffix indicates the tape-and-reel packaging format intended for automated assembly processes. Ensure compliance with RoHS standards and check the moisture sensitivity level rating prior to soldering.

Selection Notes

Select this component when a CMOS decoder requires direct compatibility with TTL logic levels without additional interface circuitry. The HCT technology provides performance comparable to LS-TTL while maintaining lower power consumption. Verify that the system supply voltage remains strictly within the 4.5 V to 5.5 V recommended operating conditions to ensure correct logic thresholds.

Part Context

This device belongs to the SNx4HCT138 family of 3-to-8 line decoders produced by Texas Instruments. The 'HCT' designation signifies High-Speed CMOS technology optimized for operation with standard TTL input voltages. The 'D' suffix specifically identifies the SOIC (Small Outline Integrated Circuit) package variant designed for surface-mount technology applications.

Replacement Considerations

SN74HCT138DRG4

FAQ

How many enable inputs does the SN74HCT138DR have?

The device incorporates three enable inputs: two active-low (G2A and G2B) and one active-high (G1).

What is the function of the enable inputs?

The enable inputs allow the selection of one of eight output lines based on the binary-select inputs or can be used as a data input for demultiplexing applications.