SN74HCT138DT

Overview

The SN74HCT138DT is a 3-line to 8-line decoder/demultiplexer from the HCT logic family, housed in a 16-pin SOIC package. It operates within a supply voltage range of 4.5 V to 5.5 V and supports an industrial temperature range of -40°C to +85°C. The device features three binary select inputs (A, B, C) and three enable inputs (G1, G2A, G2B). Propagation delay times are typically 17 ns at 5.5 V for address inputs and 18 ns for enable inputs. Outputs can drive up to 10 LSTTL loads with low input current.

Feature Summary

• Designed for high-performance memory decoding and data routing applications requiring short propagation delays.
• Incorporates three enable inputs to simplify cascading and demultiplexing functions without external gates.
• Inputs are TTL-voltage compatible, allowing direct interfacing with standard TTL logic systems.

Applications

• High-speed memory address decoding
• Data transmission systems
• System routing applications

Procurement Notes

Verify the obsolete status of the SN74HCT138DT part number before procurement planning. Consult Texas Instruments for current availability or recommended active replacements such as the SN74HCT138DR. Ensure that design-in decisions account for potential supply chain constraints associated with discontinued components.

Selection Notes

Select this component when TTL-compatible inputs are required alongside CMOS performance levels. The HCT series provides speed comparable to LS-TTL while maintaining lower power consumption. Verify that the 16-pin SOIC package dimensions fit the target PCB layout and that the operating temperature range meets environmental requirements.

Part Context

This device belongs to the SNx4HCT138 family of 3-to-8 line decoders manufactured by Texas Instruments. It is part of the broader 74-series logic ecosystem, specifically optimized for high-speed digital applications. The 'DT' suffix indicates the specific SOIC package variant, which is distinct from other available packages like PDIP or TSSOP.

Replacement Considerations

The SN74HCT138DT is listed as obsolete. Active alternatives include SN74HCT138DR (SOIC), SN74HCT138PWR (TSSOP), and SN74HCT138NSR (SOP). These parts maintain functional compatibility but may differ in packaging or manufacturing revisions.