SN54HCT138, SN74HCT138
3-LINE TO 8-LINE DECODERS/DEMULTIPLEXERS
SCLS171C – MARCH 1984 – REVISED MAY 1997
SN54HCT138 . . . J OR W PACKAGE
SN74HCT138 . . . D, N, OR PW PACKAGE
(TOP VIEW)
Inputs Are TTL-Voltage Compatible
Designed Specifically for High-Speed
Memory Decoders and Data Transmission
Systems
A
B
V
CC
1
2
3
4
5
6
7
8
16
15
14
13
Y0
Y1
Y2
Incorporate Three Enable Inputs to Simplify
Cascading and/or Data Reception
C
G2A
G2B
G1
Package Options Include Plastic
Small-Outline (D), Thin Shrink
Small-Outline (PW), and Ceramic Flat (W)
Packages, Ceramic Chip Carriers (FK), and
Standard Plastic (N) and Ceramic (J)
300-mil DIPs
12 Y3
11
10
9
Y4
Y5
Y6
Y7
GND
SN54HCT138 . . . FK PACKAGE
(TOP VIEW)
description
The ’HCT138 are designed for high-performance
memory-decoding or data-routing applications
requiring very short propagation delay times. In
high-performance memory systems, these
decoders can minimize the effects of system
decoding. When employed with high-speed
memories utilizing a fast enable circuit, the delay
timesofthesedecodersandtheenabletimeofthe
memory are usually less than the typical access
time of the memory. This means that the effective
system delay introduced by the decoders is
negligible.
3
2
1
20 19
18
Y1
Y2
NC
C
G2A
NC
4
5
6
7
8
17
16
15 Y3
14
9 10 11 12 13
G2B
G1
Y4
NC – No internal connection
The conditions at the binary-select inputs and the three enable inputs select one of eight output lines. Two
active-low (G) and one active-high (G) 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.
The SN54HCT138 is characterized for operation over the full military temperature range of –55°C to 125°C. The
SN74HCT138 is characterized for operation from –40°C to 85°C.
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
Copyright 1997, Texas Instruments Incorporated
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.
1
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