3-line to 8-line decoder / demultiplexer - SN74LS138

SN74LS138 (ACTIVE)

3-line to 8-line decoder / demultiplexer

Description

These Schottky-clamped TTL MSI circuits are 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. When employed with high-speed memories utilizing a fast enable circuit, the delay times of these decoders and the enable time of the memory are usually less than the typical access time of the memory. This means that the effective system delay introduced by the Schottky-clamped system decoder is negligible.

The 'LS138, SN54S138, and SN74S138A 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 reduce the need for external gates or inverters when expanding. A 24-line decoder can be implemented without external inverters and a 32-line decoder requires only one inverter. An enable input can be used as a data input for demultiplexing applications.

All of these decoder/demultiplexers feature fully buffered inputs, each of which represents only one normalized load to its driving circuit. All inputs are clamped with high-performance Schottky diodes to suppress line-ringing and to simplify system design.

The SN54LS138 and SN54S138 are characterized for operation over the full military temperature range of -55°C to 125°C. The SN74LS138 and SN74S138A are characterized for operation from 0°C to 70°C.

 

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

 

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Other qualified versions of SN74LS138

Version Part Number Definition
Military SN54LS138 QML certified for Military and Defense Applications

Parametrics Compare all products in Decoder/Encoder/Multiplexer

 
Technology Family
VCC (Min) (V)
VCC (Max) (V)
Channels (#)
Voltage (Nom) (V)
F @ Nom Voltage (Max) (Mhz)
ICC @ Nom Voltage (Max) (mA)
tpd @ Nom Voltage (Max) (ns)
Configuration
Function
Type
Input Type
Output Type
Output Drive (IOL/IOH) (Max) (mA)
Bits (#)
Rating
Operating Temperature Range (C)
Pin/Package
Approx. Price (US$)
SN74LS138 SN54LS138
LS     LS    
4.75     4.5    
5.25     5.5    
1      
5      
35      
10      
41      
3:8      
Decoder/Demultiplexer      
Standard      
TTL      
TTL      
8/-0.4      
8      
Catalog     Military    
0 to 70     -55 to 125    
16PDIP
16SO
16SOIC    
16CDIP
16CFP
20LCCC    
0.43 | 1ku      
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