MC74AC138N

Overview

The MC74AC138N is a high-speed 1-of-8 decoder/demultiplexer manufactured by onsemi. It accepts three binary weighted inputs (A0, A1, A2) and provides eight mutually exclusive active-LOW outputs (O0-O7). The device operates within a supply voltage range of 2.0 V to 6.0 V and features three enable inputs: two active-LOW (E1, E2) and one active-HIGH (E3). It utilizes a PDIP-16 package with through-hole mounting capabilities.

Feature Summary

• Demultiplexing capability using enable inputs as data or strobe signals
• Multiple input enables allow parallel expansion to larger decoders
• Active LOW mutually exclusive outputs for precise addressing

Applications

• High-speed bipolar memory chip select address decoding
• Parallel expansion to 1-of-24 or 1-of-32 decoders
• General-purpose demultiplexing in digital logic circuits

Procurement Notes

Verify the specific ordering suffix 'N' confirms the PDIP-16 package type. Confirm RoHS compliance status as datasheets may distinguish between standard and Pb-free variants. Check lifecycle status as this component may be discontinued or subject to long lead times. Ensure the application environment matches the specified operating temperature range.

Selection Notes

Select the MC74AC138N when a 1-of-8 decoding function with active-LOW outputs is required. Choose this part over the ACT variant if TTL-compatible inputs are not necessary. Consider the PDIP-16 package only if through-hole assembly is mandated. Verify that the system power supply falls within the 2V to 6V operational range.

Part Context

This component belongs to the 74AC logic family, designed for high-speed applications compared to standard 74LS series devices. It is part of a broader line including the MC74ACT138, which offers TTL-compatible inputs. The N suffix specifically denotes the plastic dual in-line package configuration used in this product number.

Replacement Considerations

MC74ACT138N

FAQ

How can the MC74AC138N be expanded to decode more lines?

It supports parallel expansion to a 1-of-24 decoder using three devices or a 1-of-32 decoder using four devices and one inverter via its multiple enable inputs.

What is the function of the enable inputs?

The device has two active-LOW enables (E1, E2) and one active-HIGH enable (E3). All outputs remain HIGH unless E1 and E2 are LOW and E3 is HIGH.