Decoder (74LS138) Datasheet

1. Overview

The 74LS138 is a 3-to-8 line decoder/demultiplexer. It converts binary information from 3 input lines to a maximum of 8 unique output lines. It is used in digital circuits to decode binary numbers and to route signals to various outputs.

2. General Specifications

Specification	Description
Type	3-to-8 Line Decoder / Demultiplexer
Applications	Binary decoding, Data routing, Address decoding
Package Types	DIP-16, SOIC-16, TSSOP-16
Operating Temperature	0°C to +70°C
Supply Voltage	4.75V to 5.25V

3. Features

• Decodes a 3-bit binary number to 8 unique outputs.
• Active low outputs.
• High-speed operation.
• Low power consumption.
• TTL-compatible inputs and outputs.

4. Electrical Characteristics

Parameter	Value
Supply Voltage (VCC)	4.75V - 5.25V
Input Voltage (VIH)	2.0V (min)
Input Voltage (VIL)	0.8V (max)
Output Voltage (VOH)	2.4V (min)
Output Voltage (VOL)	0.5V (max)
Max Propagation Delay	14 ns (typ)
Max Input Capacitance	10 pF
Max Output Current	8 mA (max)

5. Functional Description

5.1. Block Diagram

5.2. Truth Table

Inputs	Outputs
A, B, C	Y0 - Y7
000	Y0 = LOW, Y1-Y7 = HIGH
001	Y1 = LOW, Y0, Y2-Y7 = HIGH
010	Y2 = LOW, Y0-Y1, Y3-Y7 = HIGH
011	Y3 = LOW, Y0-Y2, Y4-Y7 = HIGH
100	Y4 = LOW, Y0-Y3, Y5-Y7 = HIGH
101	Y5 = LOW, Y0-Y4, Y6-Y7 = HIGH
110	Y6 = LOW, Y0-Y5, Y7 = HIGH
111	Y7 = LOW, Y0-Y6 = HIGH

6. Pin Configuration

Pin Number	Pin Name	Description
1	GND	Ground
2	Y0	Output 0
3	Y1	Output 1
4	Y2	Output 2
5	Y3	Output 3
6	Y4	Output 4
7	Y5	Output 5
8	Y6	Output 6
9	Y7	Output 7
10	A	Input A
11	B	Input 7. Typical Application Circuits 7.1. 3-to-8 Decoder Application Circuit 8. Manufacturer Information Manufacturer Part Number Website Texas Instruments 74LS138 TI NXP Semiconductors 74LS138 NXP ON Semiconductor 74LS138 ON Semi 9. References TI 74LS138 Datasheet NXP 74LS138 Datasheet ON Semiconductor 74LS138 Datasheet