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  • Contents

Description

74LS138 is a 3-line to 8-line decoder / demultiplexer. The chip is designed to be used in high-performance memory-decoding or data-routing applications, requiring very short propagation delay times. In high performance memory systems these decoders can be used to minimize the effects of system decoding. The three enable pins of chip (in which Two active-low and one active-high) reduce the need for external gates or inverters when expanding. A 24-line decoder can be implemented with no external inverters, and a 32-line decoder requires only one inverter.

74LS138 is used in de-multiplexing applications by using enable pin as data input pin. Also the chip inputs are clamped with high-performance Schottky diodes to suppress line-ringing and simplify system design.

Catalog

Description

Catalog

CAD Models

Features

Application

Pinout  

Logic Diagram

Package

Parameters

Product Compliance

Component Datasheet

Product Manufacturer

FAQ

Ordering & Quantity

CAD Models

74LS138 Symbol

74LS138 Footprint

Features

  • Designed Specifically for High-Speed:
    • Memory Decoders
    • Data Transmission Systems
  • 3 Enable Inputs to Simplify Cascading and/or Data Reception
  • Schottky-Clamped for High Performance

Application

  • Line decoders
  • Servers
  • Digital systems
  • Line De-multiplexing
  • Telecom circuits
  • Memory circuits

Pinout

Pin Function

Pin

Name

Description

1

A0

Address input pin

2

A1

Address input pin

3

A2

Address input pin

4

E1

Enable input (active LOW)

5

E2

Enable input (active LOW)

6

E3

Enable input (active HIGH)

7

O7

Output pin 7

8

GND

Ground

9

O6

Output pin 6

10

O5

Output pin 5

11

O4

Output pin 4

12

O3

Output pin 3

13

O2

Output pin 2

14

O1

Output pin 1

15

O0

Output pin 0

16

VCC

Power supply pin

Logic Diagram

Package

Parameters

Function

Decoder, Demultiplexer

Technology Family

LS

VCC (Min) (V)

4.75

VCC (Max) (V)

5.25

Channels (#)

1

Voltage (Nom) (V)

5

F @ nom voltage (Max) (MHz)

35

ICC @ nom voltage (Max) (mA)

10

tpd @ nom Voltage (Max) (ns)

41

Configuration

3:8

Product type

Standard

IOL (Max) (mA)

8

IOH (Max) (mA)

-0.4

Rating

Catalog

Operating temperature range (C)

0 to 70

Bits (#)

8

Digital input leakage (Max) (uA)

5

ESD CDM (kV)

0.75

ESD HBM (kV)

2

Product Compliance

ECCN

EAR99

USHTS

8542390001

Component Datasheet

Datasheet

74LS138 Datasheet

Product Manufacturer

Texas Instruments Inc. (TI) is an American technology company that designs and manufactures semiconductors and various integrated circuits, which it sells to electronics designers and manufacturers globally. Its headquarters are in Dallas, Texas, United States. TI is one of the top ten semiconductor companies worldwide, based on sales volume. Texas Instruments's focus is on developing analog chips and embedded processors, which accounts for more than 80% of their revenue. TI also produces TI digital light processing (DLP) technology and education technology products including calculators, microcontrollers and multi-core processors. To date, TI has more than 43,000 patents worldwide.


FAQ

 

  • What is the difference between 74hc138 and 74LS138?

Both have the same function. 74HC138 is made of high-speed CMOS process, with low power consumption, high output, low level and wide range.

74LS138 adopts the early bipolar process, and its driving capability is relatively larger.

  • What is the functional difference between 74ls138 decoder and 74ls148?

74ls138 is a 3-8 wire decoder/multiplexer, 74ls148 is an 8-3 wire octal priority encoder.

One is decoding and the other is encoding. Opposite effect

  • What's the difference between 74LS138D and 74LS138N?

Those two are the same chip, D is SOP package, N is DIP package.

  • What are the output characteristics of 74LS138 decoder?

Under the premise that the enable terminals S1 (active high), S2 (active low), and S3 (active low) are valid at the same time, only one output terminal is low at a time (the rest are high);

If the enable terminal is invalid, the output is all high level.

  • What do the letters and numbers in 74ls138 stand for?

74ls138 is a 3-8-line decoder. The number 74 represents the 74 series of the 54/74 series, and the 74 series has an operating temperature of 0 degrees to 70 degrees. LS is a series, representing the low-power Schottky series. 138 is the variety code.

  • Whats the working principle of 74ls138?

74LS138 working principle

① When one strobe terminal (E1) is high level, and the other two strobe terminals (E2) and (E3) are low level, at the output terminals corresponding to Y0 to Y7, the binary code of address terminals (A0, A1, A2)  can be decoded at low level. For example: when A2A1A0=110, the Y6 output terminal outputs a low-level signal.

②Using E1, E2 and E3, it can be cascaded to expand into a 24-line decoder; if an external inverter is connected, it can also be cascaded to expand into a 32-line decoder.

③If one of the strobe terminals is used as a data input terminal, 74LS138 can also be used as a data distributor.

④It can be used in 8086 decoding circuit to expand memory.

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