The 74HC138 is a 3:8 Decoder IC which is, it can control 8 output pins (Y0 to Y7) by just using three address pins (A0 to A2) as inputs. The IC also has 3 Enable pins which can be used to cascade more than 1 IC to control more output pins. The IC is used in application where there is a constraint for GPIO pin on the Microcontroller and multiple peripheral control is required. The specification of the IC is give below:

74HC138 IC Specifications and Features 

• Operating Voltage: 2V to 6V
  
• Input rise and fall time: 500nS @ 4.5Vcc
  
• Minimum high level input voltage: 3.15V @ 4.5Vcc
  
• Maximum low level input voltage: 1.35V @ 4.5Vcc
  
• Sinks or sources 8 mA at VCC = 4.5V
  
• CMOS low power consumption
  
• Schmitt Trigger Action at All Inputs