SN74HCT138PWR

Overview

The SN74HCT138PWR is a 3-line to 8-line decoder/demultiplexer manufactured by Texas Instruments in the HCT logic series. It operates within a supply voltage range of 4.5 V to 5.5 V and features three binary select inputs (A, B, C) and three enable inputs (G1, G2A, G2B). The device provides eight active-low outputs capable of driving up to ten LSTTL loads with ±4-mA output drive at 5 V. Typical propagation delay is 17 ns, with maximum delays reaching 45 ns at 4.5 V. It consumes a maximum supply current of 80 µA and has a low input current of 1 µA max. The component is housed in a 16-pin TSSOP package and supports an operating temperature range from -40 °C to +85 °C.

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 cascading without external inverters.
• Inputs are TTL-voltage compatible, allowing direct interfacing with TTL logic systems.
• Outputs can drive up to 10 LSTTL loads while maintaining low power consumption.

Applications

• High-speed memory address decoding
• Data transmission systems
• Demultiplexing applications using enable inputs as data inputs

Procurement Notes

Verify the specific ordering suffix 'PWR' corresponds to the TSSOP-16 package and tape-and-reel carrier format. Confirm RoHS compliance status and lead finish details via the manufacturer's latest orderable addendum. Ensure the procurement channel sources production-active parts rather than obsolete variants like the tube-packaged 'PW'. Check moisture sensitivity level ratings for storage and reflow requirements.

Selection Notes

Select this component when TTL-compatible inputs are required alongside CMOS performance levels. The HCT series offers speed comparable to Low-Power Schottky TTL but with lower power dissipation. Consider the three enable inputs for system expansion needs, which reduce the requirement for additional logic gates during cascading operations compared to devices with fewer control pins.

Part Context

This device belongs to the SNx4HCT138 family of 3-line to 8-line decoders. It is part of Texas Instruments' standard catalog line, distinct from the military-grade SN54HCT138 variant. The HCT technology bridges the gap between standard CMOS and TTL logic families, providing necessary voltage compatibility for legacy systems while utilizing modern CMOS fabrication processes.

Replacement Considerations

SN74HCT138DR (SOIC package)

FAQ

How many enable inputs does the SN74HCT138PWR have?

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

Can unused inputs be left floating?

No, all unused inputs must be held at VCC or GND to ensure proper device operation and prevent undefined operational states.