DM74ALS138 3 to 8 Line Decoder/Demultiplexer
September 1986
Revised February 2000
DM74ALS138
3 to 8 Line Decoder/Demultiplexer
General Description
These Schottky-clamped 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
used with high-speed memories, the delay times of these
decoders are usually less than the typical access time of
the memory. This means that the effective system delay
introduced by the decoder is negligible.
The DM74ALS138 decodes one-of-eight lines, based upon
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 invert-
ers when expanding. A 24-line decoder can be imple-
mented with no external inverters, and 32-line decoder
requires only one inverter. An enable input can be used as
a data input for demultiplexing applications.
This decoder/demultiplexer features fully buffered inputs,
presenting only one normalized load to its driving circuit. All
inputs are clamped with high-performance Schottky diodes
to suppress line-ringing and simplify system design.
Features
s
Designed specifically for high speed:
Memory decoders
Data transmission systems
s
3- to 8-line decoder incorporates 3 enable inputs to sim-
plify cascading and/or data reception
s
Low power dissipation…23 mW typ
s
Switching specifications guaranteed over full tempera-
ture and V
CC
range
s
Advanced oxide-isolated, ion-implanted Schottky TTL
process
Ordering Code:
Order Number
DM74ALS138M
DM74ALS138SJ
DM74ALS138N
Package Number
M16A
M16D
N16E
Package Description
16-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-012, 0.150 Narrow
16-Lead Small Outline Package (SOP), EIAJ TYPE II, 5.3mm Wide
16-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300 Wide
Devices also available in Tape and Reel. Specify by appending the suffix letter “X” to the ordering code.
Connection Diagram
Function Table
Enable
Inputs
G1
X
L
H
H
H
H
H
H
H
H
C
G2
(Note 1)
H
X
L
L
L
L
L
L
L
L
X
X
L
L
L
L
H
H
H
H
Select
Inputs
B
X
X
L
L
H
H
L
L
H
H
Outputs
A Y0 Y1 Y2 Y3 Y4 Y5 Y6 Y7
X
X
L
H
L
H
L
H
L
H
H
H
L
H
H
H
H
H
H
H
H
H
H
L
H
H
H
H
H
H
H
H
H
H
L
H
H
H
H
H
H
H
H
H
H
L
H
H
H
H
H
H
H
H
H
H
L
H
H
H
H
H
H
H
H
H
H
L
H
H
H
H
H
H
H
H
H
H
L
H
H
H
H
H
H
H
H
H
H
L
Note 1:
G2
=
G2A
+
G2B
© 2000 Fairchild Semiconductor Corporation
DS006111
www.fairchildsemi.com
DM74ALS138
Absolute Maximum Ratings
(Note 2)
Supply Voltage
Input Voltage
Operating Free Air Temperature Range
Storage Temperature Range
Typical
θ
JA
N Package
M Package
75.5°C/W
104.0°C/W
7V
7V
0°C to
+70°C
−65°C
to
+150°C
Note 2:
The “Absolute Maximum Ratings” are those values beyond which
the safety of the device cannot be guaranteed. The device should not be
operated at these limits. The parametric values defined in the Electrical
Characteristics tables are not guaranteed at the absolute maximum ratings.
The “Recommended Operating Conditions” table will define the conditions
for actual device operation.
Recommended Operating Conditions
Symbol
V
CC
V
IH
V
IL
I
OH
I
OL
T
A
Supply Voltage
HIGH Level Input Voltage
LOW Level Input Voltage
HIGH Level Output Current
LOW Level Output Current
Free Air Operating Temperature
0
Parameter
Min
4.5
2
0.8
−0.4
8
70
Nom
5
Max
5.5
Units
V
V
V
mA
mA
°C
Electrical Characteristics
over recommended operating free air temperature range. All typical values are measured at V
CC
=
5V, T
A
=
25°C.
Symbol
V
IK
V
OH
V
OL
I
I
I
IH
I
IL
I
O
I
CC
Parameter
Input Clamp Voltage
HIGH Level
Output Voltage
LOW Level
Output Voltage
Input Current @ Max.
Input Voltage
HIGH Level Input Current
LOW Level Input Current
Output Drive Current
Supply Current
I
OH
= −0.4
mA
V
CC
=
4.5V to 5.5V
V
CC
=
4.5V
V
CC
=
5.5V, V
IH
=
7V
V
CC
=
5.5V, V
IH
=
2.7V
V
CC
=
5.5V, V
IL
=
0.4V
V
CC
=
5.5V
V
CC
=
5.5V
V
O
=
2.25V
−30
5
I
OL
=
8 mA
0.35
0.5
0.1
20
−0.1
−112
10
V
mA
µA
mA
mA
mA
Conditions
V
CC
=
4.5V, I
I
= −18
mA
V
CC
−
2
Min
Typ
Max
−1.5
Units
V
V
Switching Characteristics
over recommended operating free air temperature range.
Symbol
t
PLH
t
PHL
t
PLH
t
PHL
Parameter
Propagation Delay Time
LOW-to-HIGH Level Output
Propagation Delay Time
HIGH-to-LOW Level Output
Propagation Delay Time
LOW-to-HIGH Level Output
Propagation Delay Time
HIGH-to-LOW Level Output
Conditions
V
CC
=
4.5V to 5.5V
R
L
=
500Ω
C
L
=
50 pF
From (Input)
To (Output)
A, B, C
to Y
A, B, C
to Y
Enable
to Y
Enable
to Y
Min
6
6
4
5
Max
22
18
17
17
Units
ns
ns
ns
ns
3
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