74LS138 3 to 8 Decoder/Demultiplexer


The 74LS series of integrated circuits (ICs) was one of the most popular logic families of transistor-transistor logic (TTL) logic chips. 74LS series is a bipolar, low-power Schottky IC. The 74LS138, decode one of eight lines dependent on the conditions at the three binary select inputs and the three enable inputs. Two active-low and one active-high enable inputs to reduce the need for external gates or inverters when expanding

74LS138 Features

  • Decodes One-of-Eight Lines Based Upon the Select Inputs
  • Inputs Clamped with Schottky Diodes
  • Designed for Memory Decoders and Data Transmission Systems
  • Operating Temperature up to 70°C
  • Standard TTL Switching Voltages

74LS138 Specifications

Supply Voltage4.75 – 5.25Vdc
Maximum Clock Frequency40Mhz
Power Dissipation2mW/gate @100kHz
Minimum Output Current8mA
Propagation Delay10nS
Fan Out (TTL Loads)20

74LS138 Pinout Diagram

74LS138 Pin Description

Pin NoPin NameDescription
1A0Data Input Select Pin
2A1Data Input Select Pin
3A2Data Input Select Pin
4E1Enable Pin
5E2Enable Pin
6E3Enable Pin
7O7Output 7
9O6Output 6
10O5Output 5
11O4Output 4
12O3Output 3
13O2Output 2
14O1Output 1
15O0Output 0
16VCCPositive Supply

74LS138 Circuit


  • Decoders are used to input data to a specified output line as is done in addressing core memory where input data is to be stored in a specified memory location.
  • It is used in code conversions.
  • In high-performance memory systems, this decoder can be used to minimize the effects of system decoding

74LS138 Alternative Equivalent


Download 74LS138 3 to 8 Decoder/Demultiplexer Datasheet from the link given below.