TC74HC138APF

Overview

The TC74HC138APF is a high-speed CMOS 3-to-8 line decoder manufactured using silicon gate C2MOS technology. It provides eight active-low outputs (0Y to 7Y) controlled by three binary select inputs (A, B, and C). The device features three enable inputs (G1, 2AG, 2BG) for cascading or memory address decoding. It operates within a supply voltage range of 2 V to 6 V and supports an operating temperature from -40°C to +85°C. Key electrical parameters include a typical propagation delay of 16 ns at 5 V, a maximum quiescent current of 4 μA, and symmetrical output drive capability of 4 mA minimum.

Feature Summary

• High-speed operation comparable to equivalent LSTTL while maintaining low power dissipation.
• Provides three enable inputs to facilitate cascade connections and memory address decoding functions.
• Features balanced propagation delays with symmetrical output impedance for both high and low states.
• Includes protection circuits on all inputs against static discharge and transient excess voltage.

Applications

• Memory address decoding in computer systems
• Data routing applications
• General electronics equipment

Procurement Notes

Verify the specific package type upon ordering, as the 'PF' suffix indicates a 16-pin DIP package. Confirm RoHS compliance status directly with Toshiba Semiconductor and Storage representatives, as environmental declarations are subject to change. Ensure design reviews cover reliability derating concepts per the Toshiba Semiconductor Reliability Handbook before finalizing procurement specifications.

Selection Notes

Select this component when a 3-to-8 decoder is required with LSTTL pin compatibility and CMOS power efficiency. It is suitable for designs needing wide voltage operation between 2 V and 6 V. Consider the DIP-16 package for through-hole mounting requirements. Verify that the application does not involve unintended uses such as aerospace or medical equipment where higher reliability standards apply.

Part Context

This part belongs to the TC74HC138A series of 3-to-8 line decoders produced by Toshiba Semiconductor and Storage. The family includes variants like TC74HC138AF and TC74HC138AFN, which differ primarily in packaging styles such as SOP and SOL. These devices are designed to replace older logic families while offering improved speed and lower power consumption characteristics.

Replacement Considerations

The datasheet explicitly notes pin and function compatibility with the 74LS138 series. Designers replacing legacy TTL components should verify signal levels and drive capabilities match the new CMOS specifications.

FAQ

How do the enable inputs control the decoding function?

Decoding occurs only when G1 is held high and both 2AG and 2BG are held low. If G1 is low or either 2AG or 2BG is high, the function is inhibited and all outputs go high.

What is the typical propagation delay time?

The typical propagation delay time (tpd) is 16 ns when measured at a supply voltage (VCC) of 5 V.