2000 Fairchild Semiconductor Corporation
DS006111
www.fairchildsemi.com
September 1986
Revised February 2000
DM74ALS138 3 to 8
Li
ne Decoder/
D
emult
i
pl
exer
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:
Devices also available in Tape and Reel. Specify by appending the suffix letter "X" to the ordering code.
Connection Diagram
Function Table
Note 1: G2
=
G2A
+
G2B
Order Number
Package Number
Package Description
DM74ALS138M
M16A
16-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-012, 0.150 Narrow
DM74ALS138SJ
M16D
16-Lead Small Outline Package (SOP), EIAJ TYPE II, 5.3mm Wide
DM74ALS138N
N16E
16-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300 Wide
Enable
Select
Outputs
Inputs
Inputs
G1
G2
(Note 1)
C
B
A Y0 Y1 Y2 Y3 Y4 Y5 Y6 Y7
X
H
X
X
X
H
H
H
H
H
H
H
H
L
X
X
X
X
H
H
H
H
H
H
H
H
H
L
L
L
L
L
H
H
H
H
H
H
H
H
L
L
L
H
H
L
H
H
H
H
H
H
H
L
L
H
L
H
H
L
H
H
H
H
H
H
L
L
H
H
H
H
H
L
H
H
H
H
H
L
H
L
L
H
H
H
H
L
H
H
H
H
L
H
L
H
H
H
H
H
H
L
H
H
H
L
H
H
L
H
H
H
H
H
H
L
H
H
L
H
H
H
H
H
H
H
H
H
H
L
3
www.fairchildsemi.com
DM74ALS138
Absolute Maximum Ratings
(Note 2)
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
Electrical Characteristics
over recommended operating free air temperature range. All typical values are measured at V
CC
=
5V, T
A
=
25
C.
Switching Characteristics
over recommended operating free air temperature range.
Supply Voltage
7V
Input Voltage
7V
Operating Free Air Temperature Range
0
C to
+
70
C
Storage Temperature Range
-
65
C to
+
150
C
Typical
JA
N Package
75.5
C/W
M Package
104.0
C/W
Symbol
Parameter
Min
Nom
Max
Units
V
CC
Supply Voltage
4.5
5
5.5
V
V
IH
HIGH Level Input Voltage
2
V
V
IL
LOW Level Input Voltage
0.8
V
I
OH
HIGH Level Output Current
-
0.4
mA
I
OL
LOW Level Output Current
8
mA
T
A
Free Air Operating Temperature
0
70
C
Symbol
Parameter
Conditions
Min
Typ
Max
Units
V
IK
Input Clamp Voltage
V
CC
=
4.5V, I
I
=
-
18 mA
-
1.5
V
V
OH
HIGH Level
I
OH
=
-
0.4 mA
V
CC
-
2
V
Output Voltage
V
CC
=
4.5V to 5.5V
V
OL
LOW Level
V
CC
=
4.5V
I
OL
=
8 mA
0.35
0.5
V
Output Voltage
I
I
Input Current @ Max.
V
CC
=
5.5V, V
IH
=
7V
0.1
mA
Input Voltage
I
IH
HIGH Level Input Current
V
CC
=
5.5V, V
IH
=
2.7V
20
A
I
IL
LOW Level Input Current
V
CC
=
5.5V, V
IL
=
0.4V
-
0.1
mA
I
O
Output Drive Current
V
CC
=
5.5V
V
O
=
2.25V
-
30
-
112
mA
I
CC
Supply Current
V
CC
=
5.5V
5
10
mA
Symbol
Parameter
Conditions
From (Input)
Min
Max
Units
To (Output)
t
PLH
Propagation Delay Time
V
CC
=
4.5V to 5.5V
A, B, C
6
22
ns
LOW-to-HIGH Level Output
R
L
=
500
to Y
t
PHL
Propagation Delay Time
C
L
=
50 pF
A, B, C
6
18
ns
HIGH-to-LOW Level Output
to Y
t
PLH
Propagation Delay Time
Enable
4
17
ns
LOW-to-HIGH Level Output
to Y
t
PHL
Propagation Delay Time
Enable
5
17
ns
HIGH-to-LOW Level Output
to Y
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