CD74HCT138M

Overview

The CD74HCT138M is a high-speed CMOS logic decoder manufactured by Texas Instruments. It functions as a 3-to-8 line decoder/demultiplexer housed in a 16-pin SOIC package. The device operates within a supply voltage range of 4.5V to 5.5V and supports an operating temperature range from -55°C to 125°C. It features three binary select inputs (A0, A1, A2) and three enable inputs: two active-low (E1, E2) and one active-high (E3). These enables facilitate cascading multiple units. The outputs are active-low for the standard configuration.

Feature Summary

• Provides decoding functionality for memory address mapping or data routing applications using three binary select lines.
• Includes dual active-low and single active-high enable inputs to simplify system expansion through cascading.
• Features low power consumption characteristics typical of CMOS technology while maintaining speed comparable to Low-Power Schottky TTL logic.

Applications

• Memory address decoding
• Data routing
• I/O port selection

Procurement Notes

Verify that the specific suffix 'M' corresponds to the SOIC-16 package variant required for your design. Confirm RoHS compliance status and moisture sensitivity level requirements against your manufacturing process specifications. Ensure the active-low output polarity matches your circuit design needs, as the HC238 variant offers active-high outputs.

Selection Notes

Select this component when a 3-to-8 decoding function is required with direct compatibility to LSTTL input levels. The HCT series ensures logical compatibility with 5V TTL systems. Consider the wide industrial temperature range if the application operates in extreme environments. Verify that the 16-pin surface mount package fits the available PCB real estate.

Part Context

This part belongs to the Texas Instruments 74HCT logic family, which bridges CMOS low power with TTL performance. It is functionally related to the CD74HC138 but optimized for 5V operation with TTL-compatible input thresholds. The device serves as a fundamental building block for digital systems requiring signal distribution or address translation.

Replacement Considerations

CD74HC138M (HC series, different input thresholds)

FAQ

What is the logic state of the outputs?

The CD74HCT138M outputs are active-low. When enabled, only one output goes low corresponding to the binary input code, while all others remain high.

How many enable inputs does the device have?

The device has three enable inputs: two active-low inputs (E1 and E2) and one active-high input (E3). All must be in their correct states for the decoder to operate.