5-230
FAST AND LS TTL DATA
1-OF-8 DECODER/
DEMULTIPLEXER
The LSTTL/MSI SN54/74LS138 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 ex-
pansion 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 Motorola 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
CONNECTION DIAGRAM DIP (TOP VIEW)
NOTE:
The Flatpak version
has the same pinouts
(Connection Diagram) as
the Dual In-Line Package.
PIN NAMES LOADING (Note a)
HIGH LOW
A0–A2
E1, E2
E3
O0–O7
Address Inputs
Enable (Active LOW) Inputs
Enable (Active HIGH) Input
Active LOW Outputs (Note b)
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 (2.5) U.L.
NOTES:
a) 1 TTL Unit Load (U.L.) = 40 µA HIGH/1.6 mA LOW.
b) The Output LOW drive factor is 2.5 U.L. for Military (54) and 5 U.L. for Commercial (74)
Temperature Ranges.
SN54/74LS138
1-OF-8 DECODER/
DEMULTIPLEXER
LOW POWER SCHOTTKY
J SUFFIX
CERAMIC
CASE 620-09
N SUFFIX
PLASTIC
CASE 648-08
16 1
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ORDERING INFORMATION
SN54LSXXXJ Ceramic
SN74LSXXXN Plastic
SN74LSXXXD SOIC
16 1
D SUFFIX
SOIC
CASE 751B-03
LOGIC SYMBOL
LOGIC DIAGRAM
5-231
FAST AND LS TTL DATA
SN54/74LS138
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 (A0, A1, A2)
and when enabled provides eight mutually exclusive active
LOW Outputs (O0–O7). The LS138 features three Enable in-
puts, two active LOW (E1, E2) and one active HIGH (E3). All
outputs will be HIGH unless E1 and E2 are LOW and E3 is
HIGH. This multiple enable function allows easy parallel ex-
pansion 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 appropri-
ate active HIGH or active LOW state.
TRUTH TABLE
INPUTS OUTPUTS
E1E2E3A0A1A2O0O1O2O3O4O5O6O7
H X X X X X H H H H H H H H
X H X X X X H H H H H H H H
X X L X X X H H H H H H H H
L L H L L L L H H H H H H H
L L H H L L H L H H H H H H
L L H L H L H H L H H H H H
L L H H H L H H H L H H H H
L L H L L H H H H H L H H H
L L H H L H H H H H H L H H
L L H L H H H H H H H H L 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
O0O31
A0
A1
A2
A3
A4H
LS04
A0A1A2E
LS138
O0O1O2O3O4O5O6O7
A0A1A2E
LS138
O0O1O2O3O5O6O7
O4O0O1O2O3O5O6O7
O4
E
LS138
A0A1A2A0A1A2E
LS138
O0O2O3O5O6O7
O4
O1
12 3 123 12 3 12 3
Figure a
5-232
FAST AND LS TTL DATA
SN54/74LS138
GUARANTEED OPERATING RANGES
Symbol Parameter Min Typ Max Unit
VCC Supply Voltage 54
74 4.5
4.75 5.0
5.0 5.5
5.25 V
TAOperating Ambient Temperature Range 54
74 –55
025
25 125
70 °C
IOH Output Current — High 54, 74 –0.4 mA
IOL Output Current — Low 54
74 4.0
8.0 mA
DC CHARACTERISTICS OVER OPERATING TEMPERATURE RANGE (unless otherwise specified)
Symbol
Parameter
Limits
Unit
Test Conditions
Symbol
Parameter
Min Typ Max
Unit
Test Conditions
VIH Input HIGH Voltage 2.0 V Guaranteed Input HIGH Voltage for
All Inputs
VIL
Input LOW Voltage
54 0.7
V
Guaranteed Input LOW Voltage for
All Inputs
VIL
Input LOW Voltage
74 0.8
V
Guaranteed Input LOW Voltage for
All Inputs
VIK Input Clamp Diode Voltage –0.65 –1.5 V VCC = MIN, IIN = –18 mA
VOH
Output HIGH Voltage
54
2.5
3.5
V
VCC = MIN, IOH = MAX, VIN = VIH
or VIL per Truth Table
VOH
Output HIGH Voltage
54
2.5
3.5
V
VCC = MIN, IOH = MAX, VIN = VIH
or VIL per Truth Table
VOH
Output HIGH Voltage
74 2.7 3.5 V
VCC = MIN, IOH = MAX, VIN = VIH
or VIL per Truth Table
VOL
Output LOW Voltage
54, 74 0.25 0.4 V IOL = 4.0 mA
VCC = VCC MIN,
VIN = VIL or VIH
per Truth Table
VOL
Output LOW Voltage
74 0.35 0.5 V IOL = 8.0 mA
VIN = VIL or VIH
per Truth Table
IIH
Input HIGH Current
20 µA VCC = MAX, VIN = 2.7 V
IIH
Input HIGH Current
0.1 mA VCC = MAX, VIN = 7.0 V
IIL Input LOW Current –0.4 mA VCC = MAX, VIN = 0.4 V
IOS Short Circuit Current (Note 1) –20 –100 mA VCC = MAX
ICC 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 (TA = 25°C)
Symbol
Parameter
Levels of
Delay
Limits
Unit
Test Conditions
Symbol
Parameter
Levels of
Delay
Min Typ Max
Unit
Test Conditions
tPLH
tPHL Propagation Delay
Address to Output 2
213
27 20
41 ns
VCC = 5.0 V
CL = 15 pF
tPLH
tPHL Propagation Delay
Address to Output 3
318
26 27
39 ns
V
CC = 5.0 V
CL = 15 pF
tPLH
tPHL Propagation Delay E1 or E2
Enable to Output 2
212
21 18
32 ns
VCC = 5.0 V
CL = 15 pF
tPLH
tPHL Propagation Delay E3
Enable to Output 3
317
25 26
38 ns
AC WAVEFORMS
Figure 1 Figure 2
5-233
FAST AND LS TTL DATA
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5-234
FAST AND LS TTL DATA
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