1. General description
The 74AHC138; 74AHCT138 are high-speed Si-gate CMOS devices and are pin compatible with
Low power Schottky TTL (LSTTL). They are specified in compliance with JEDEC standard No. 7A.
The 74AHC138; 74AHCT138 is a 3-to-8 line decoder/demultiplexer. It accepts three binary
weighted address inputs (A0, A1 and A2) and, when enabled, provides eight mutually exclusive
outputs (Y0 to Y7) that are LOW when selected.
There are three enable inputs: two active LOW (E1 and E2) and one active HIGH (E3). Every
output will be HIGH unless E1 and E2 are LOW and E3 is HIGH.
This multiple enable function allows easy parallel expansion of the device to a 1-of-32 (5 lines to
32 lines) decoder with just four 74AHC138; 74AHCT138 devices and one inverter. The 74AHC138;
74AHCT138 can be used as an eight output demultiplexer by using one of the active LOW enable
inputs as the data input and the remaining enable inputs as strobes. Unused enable inputs must be
permanently tied to their appropriate active HIGH or LOW state.
2. Features and benefits
• Balanced propagation delays
• All inputs have Schmitt-trigger action
• Demultiplexing capability
• Multiple input enable for easy expansion
• Ideal for memory chip select decoding
• Inputs accepts voltages higher than VCC
• For 74AHC138 only: operates with CMOS input levels
• For 74AHCT138 only: operates with TTL input levels
• ESD protection:
• HBM JESD22-A114E exceeds 2000 V
• MM JESD22-A115-A exceeds 200 V
• CDM JESD22-C101C exceeds 1000 V
• Multiple package options
• Specified from -40 °C to +85 °C and from -40 °C to +125 °C