SN74HCT138D

Overview

The SN74HCT138D is a 3-line to 8-line decoder/demultiplexer manufactured by Texas Instruments in a 16-pin SOIC package. It operates within a supply voltage range of 4.5 V to 5.5 V and supports an operating temperature range of -40°C to +85°C. The device features a typical propagation delay (tpd) of 17 ns at 5.5 V, with maximum delays reaching 34 ns. Outputs can drive up to 10 LSTTL loads, providing ±4 mA output drive current at 5 V. Maximum input current is 1 µA, and the maximum supply current (ICC) is 80 µA.

Feature Summary

• Designed for high-performance memory decoding and data routing applications requiring short propagation delays.
• Incorporates three enable inputs (two active-low, one active-high) to simplify cascading and demultiplexing functions.
• Inputs are TTL-voltage compatible, allowing direct interfacing with standard logic families.

Applications

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

Procurement Notes

Verify the specific ordering suffix against the manufacturer's latest Package Option Addendum to confirm production status and material specifications. The base model SN74HCT138D is listed as obsolete; ensure the selected variant matches the required packaging and lead finish for your assembly process. Cross-reference thermal resistance values for the SOIC package during layout planning.

Selection Notes

Select this component when TTL-compatible inputs are required alongside CMOS low power consumption. The HCT series ensures compatibility with standard TTL logic levels while offering faster switching speeds than standard HC devices. Verify that the system supply voltage remains strictly between 4.5 V and 5.5 V to maintain valid logic thresholds and prevent damage.

Part Context

This device belongs to the SNx4HCT138 family of 3-line to 8-line decoders and demultiplexers. It is part of Texas Instruments' extensive line of digital logic ICs designed for general-purpose computing and industrial applications. The HCT technology combines the speed of LS-TTL with the low power of CMOS, making it suitable for battery-powered or noise-sensitive environments.

Replacement Considerations

SN74HCT138DR

FAQ

How many enable inputs does the SN74HCT138D have?

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

What is the maximum supply current for this device?

The maximum supply current (ICC) is 80 µA at 5.5 V with all inputs at VCC or GND and outputs open.