Semiconductor Components Industries, LLC, 1999
December, 1999 – Rev. 6
1 Publication Order Number:
SN74LS138/D
SN74LS138
1-of-8 Decoder/
Demultiplexer
The LSTTL/MSI SN74LS138 is a high speed 1-of-8 Decoder /
Demultiplexer. This device is ideally suited for high speed bipolar
memory chip select address decoding. The multiple input enables
allow parallel expansion to a 1-of-24 decoder using just three LS138
devices or to a 1-of-32 decoder using four LS138s and one inverter.
The LS138 is fabricated with the Schottky barrier diode process for
high speed and is completely compatible with all ON Semiconductor
TTL families.
• Demultiplexing Capability
• Multiple Input Enable for Easy Expansion
• Typical Power Dissipation of 32 mW
• Active Low Mutually Exclusive Outputs
• Input Clamp Diodes Limit High Speed Termination Effects
GUARANTEED OPERATING RANGES
Symbol Parameter Min Typ Max Unit
V
CC
Supply Voltage 4.75 5.0 5.25 V
T
A
Operating Ambient
T emperature Range
0 25 70 °C
I
OH
Output Current – High –0.4 mA
I
OL
Output Current – Low 8.0 mA
LOW
POWER
SCHOTTKY
Device Package Shipping
ORDERING INFORMATION
SN74LS138N 16 Pin DIP 2000 Units/Box
SN74LS138D 16 Pin
SOIC
D SUFFIX
CASE 751B
http://onsemi.com
2500/Tape & Reel
PLASTIC
N SUFFIX
CASE 648
16
1
16
1
SN74LS138
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2
CONNECTION DIAGRAM DIP (TOP VIEW)
Address Inputs
Enable (Active LOW) Inputs
Enable (Active HIGH) Input
Active LOW Outputs
A0 – A
2
E1, E
2
E
3
O0 – O
7
0.5 U.L.
0.5 U.L.
0.5 U.L.
10 U.L.
0.25 U.L.
0.25 U.L.
0.25 U.L.
5 U.L.
NOTES:
a) 1 TTL Unit Load (U.L.) = 40 mA HIGH/1.6 mA LOW.
HIGH LOW
(Note a)LOADING
PIN NAMES
NOTE:
The Flatpak version has the same
pinouts (Connection Diagram) as
the Dual In-Line Package.
14 13 12 1 1 10 9
123456
7
16 15
8
V
CC
O
0
GND
O1O2O3O4O5O
6
A
0
E1E2E3O
7
A1A
2
LOGIC SYMBOL
VCC = PIN 16
GND = PIN 8
15 14 13 12 11 10 9
123 456
123
A
0A1A2
E
O
0O1O2O3O4O5O6O7
7
SN74LS138
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3
LOGIC DIAGRAM
A2A
1
A
0
E1E2E
3
O7O
6
O5O4O3O2O1O
0
VCC = PIN 16
GND = PIN 8
= Pin Numbers
3 2 1 4 5 6
7
9
1514
1312
1110
SN74LS138
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4
FUNCTIONAL DESCRIPTION
The LS138 is a high speed 1-of-8 Decoder/Demultiplexer
fabricated with the low power Schottky barrier diode
process. The decoder accepts three binary weighted inputs
(A
0
, A1, A2) and when enabled provides eight mutually
exclusive active LOW Outputs (O0–O7). The LS138
features three Enable inputs, two active LOW (E1, E2) and
one active HIGH (E3). All outputs will be HIGH unless E
1
and E2 are LOW and E3 is HIGH. This multiple enable
function allows easy parallel expansion of the device to a
1-of-32 (5 lines to 32 lines) decoder with just four LS138s
and one inverter. (See Figure a.)
The LS138 can be used as an 8-output demultiplexer by
using one of the active LOW Enable inputs as the data input
and the other Enable inputs as strobes. The Enable inputs
which are not used must be permanently tied to their
appropriate active HIGH or active LOW state.
TRUTH TABLE
INPUTS OUTPUTS
E
1
E
2
E
3
A
0
A
1
A
2
O
0
O
1
O
2
O
3
O
4
O
5
O
6
O
7
H X X X X X H H H H H H H H
X HXXXXHHHHHHH H
X XLXXXHHHHHHH H
L LHLLLLHHHHHH H
L LHHLLHLHHHHH H
L LHLHLHHLHHHH H
L LHHHLHHHLHHH H
L LHLLHHHHHLHH H
L LHHLHHHHHHLH H
L LHLHHHHHHHHL H
L L H H H H H H H H H H H L
H = HIGH Voltage Level
L = LOW Voltage Level
X = Don’t Care
O
0
O
31
A
0
A
1
A
2
A
3
A
4
H
LS04
A
0A1A2
E
LS138
O
0O1O2O3O4O5O6O7
LS138
123 123 123 123
Figure a
LS138 LS138
A
0A1A2
E
O
0O1O2O3O4O5O6O7
A0A1A
2
E
O
0O1O2O3O4O5O6O7
A0A1A
2
E
O
0O1O2O3O4O5O6O7
SN74LS138
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5
DC CHARACTERISTICS OVER OPERATING TEMPERATURE RANGE (unless otherwise specified)
Limits
Symbol Parameter
Min Typ Max
Unit Test Conditions
V
IH
Input HIGH Voltage 2.0 V
Guaranteed Input HIGH Voltage for
All Inputs
V
IL
Input LOW Voltage
0.8
V
Guaranteed Input LOW Voltage for
All Inputs
V
IK
Input Clamp Diode Voltage –0.65 –1.5 V VCC = MIN, IIN = –18 mA
V
OH
Output HIGH Voltage
2.7 3.5 V VCC = MIN, IOH = MAX, VIN = V
IH
or VIL per Truth Table
p
0.25 0.4 V IOL = 4.0 mA
VCC = VCC MIN,
VOLOutput LOW Voltage
0.35 0.5 V IOL = 8.0 mA
V
IN
=
V
IL
or
V
IH
per Truth Table
p
20 µA VCC = MAX, VIN = 2.7 V
IIHInput HIGH Current
0.1 mA VCC = MAX, VIN = 7.0 V
I
IL
Input LOW Current –0.4 mA VCC = MAX, VIN = 0.4 V
I
OS
Short Circuit Current (Note 1) –20 –100 mA VCC = MAX
I
CC
Power Supply Current 10 mA VCC = MAX
Note 1: Not more than one output should be shorted at a time, nor for more than 1 second.
AC CHARACTERISTICS (T
A
= 25°C)
Levels of
Limits
Symbol Parameter
Levels of
Delay
Min Typ Max
Unit T est Conditions
t
PLH
t
PHL
Propagation Delay
Address to Output
2
2
13
27
20
41
ns
t
PLH
t
PHL
Propagation Delay
Address to Output
3
3
18
26
27
39
ns
VCC = 5.0 V
t
PLH
t
PHL
Propagation Delay E1 or E
2
Enable to Output
2
2
12
21
18
32
ns
CC
CL = 15 pF
t
PLH
t
PHL
Propagation Delay E
3
Enable to Output
3
3
17
25
26
38
ns
AC WAVEFORMS
Figure 1. Figure 2.
V
IN
V
OUT
1.3 V
t
PHL
1.3 V
1.3 V
1.3 V
t
PLH
V
IN
V
OUT
1.3 V
t
PHL
1.3 V
t
PLH
1.3 V
1.3 V
SN74LS138
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6
P ACKAGE DIMENSIONS
N SUFFIX
PLASTIC PACKAGE
CASE 648–08
ISSUE R
NOTES:
1. DIMENSIONING AND TOLERANCING PER ANSI
Y14.5M, 1982.
2. CONTROLLING DIMENSION: INCH.
3. DIMENSION L TO CENTER OF LEADS WHEN
FORMED PARALLEL.
4. DIMENSION B DOES NOT INCLUDE MOLD FLASH.
5. ROUNDED CORNERS OPTIONAL.
–A–
B
F
C
S
H
G
D
J
L
M
16 PL
SEATING
18
916
K
PLANE
–T–
M
A
M
0.25 (0.010) T
DIM MIN MAX MIN MAX
MILLIMETERSINCHES
A 0.740 0.770 18.80 19.55
B 0.250 0.270 6.35 6.85
C 0.145 0.175 3.69 4.44
D 0.015 0.021 0.39 0.53
F 0.040 0.70 1.02 1.77
G 0.100 BSC 2.54 BSC
H 0.050 BSC 1.27 BSC
J 0.008 0.015 0.21 0.38
K 0.110 0.130 2.80 3.30
L 0.295 0.305 7.50 7.74
M 0 10 0 10
S 0.020 0.040 0.51 1.01
____
SN74LS138
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7
P ACKAGE DIMENSIONS
D SUFFIX
PLASTIC SOIC PACKAGE
CASE 751B–05
ISSUE J
NOTES:
1. DIMENSIONING AND TOLERANCING PER ANSI
Y14.5M, 1982.
2. CONTROLLING DIMENSION: MILLIMETER.
3. DIMENSIONS A AND B DO NOT INCLUDE
MOLD PROTRUSION.
4. MAXIMUM MOLD PROTRUSION 0.15 (0.006)
PER SIDE.
5. DIMENSION D DOES NOT INCLUDE DAMBAR
PROTRUSION. ALLOWABLE DAMBAR
PROTRUSION SHALL BE 0.127 (0.005) TOTAL
IN EXCESS OF THE D DIMENSION AT
MAXIMUM MATERIAL CONDITION.
18
16 9
SEATING
PLANE
F
J
M
R
X 45
_
G
8 PLP
–B–
–A–
M
0.25 (0.010) B
S
–T–
D
K
C
16 PL
S
B
M
0.25 (0.010) A
S
T
DIM MIN MAX MIN MAX
INCHESMILLIMETERS
A 9.80 10.00 0.386 0.393
B 3.80 4.00 0.150 0.157
C 1.35 1.75 0.054 0.068
D 0.35 0.49 0.014 0.019
F 0.40 1.25 0.016 0.049
G 1.27 BSC 0.050 BSC
J 0.19 0.25 0.008 0.009
K 0.10 0.25 0.004 0.009
M 0 7 0 7
P 5.80 6.20 0.229 0.244
R 0.25 0.50 0.010 0.019
____
SN74LS138
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8
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