© 2000 Fairchild Semiconductor Corporation DS006111 www .fairchildsemi.com
September 1986
Revised February 2000
DM74ALS138 3 to 8 Line Decoder/Demultiplexer
DM74ALS138
3 to 8 Line Decoder/Demultiplexer
General Descript ion
These Schottky-clamped circuits are de signed to be used
in high-performance memory-decoding or data-routing
applicatio ns, requiring very short propagation delay times.
In high-perf ormance me mory systems th ese decoders can
be used to minimize the effects of system de coding. 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
introd uced by the dec oder is negligi ble.
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 inp uts reduce the ne ed for externa l 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 inve rter. 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 ar e cla mp ed wi t h hig h-p er for man ce S ch ottk y diodes
to suppress line-ringing and simplify system design.
Features
Designed specifically for high speed:
Memory decoders
Data transmission systems
3- to 8-l in e d ecod er inco rporates 3 e nab l e in put s to sim-
plify cascading and/or data reception
Low power dissipation…23 mW typ
Switching specifications guaranteed over full tempera-
ture and VCC range
Advanced oxide-isolated, ion-implanted Schottky TTL
process
Ordering Code:
Devices also available in Tape and R eel. Speci fy by appending the s uffix let t er “X” to the orderin g c ode.
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 Y0Y1Y2Y3Y4Y5Y6Y7
X H XXXHHHHHHHH
L X XXXHHHHHHHH
H L LLLLHHHHHHH
H L LLHHLHHHHHH
H L LHLHHLHHHHH
H L LHHHHHLHHHH
H L HLLHHHHLHHH
H L HLHHHHHHLHH
H L HHLHHHHHHLH
H L HHHHHHHHHHL
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DM74ALS138
Logic Diagram
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DM74ALS138
Absolute Maximum Ratings(Note 2)
Note 2: The “A bsol ute M axim um Ratin gs” are those valu es b eyo nd 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 “Re comm ended Operat ing Co ndition s” table will de fine the cond itions
for actu al device operation.
Recommended Operating Conditions
Electri cal Characteristics
over recommended operating free air temperature range. All typical values are measured at VCC = 5V, TA = 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 θJA
N Package 75.5°C/W
M Package 104.0°C/W
Symbol Parameter Min Nom Max Units
VCC Supply Voltage 4.5 5 5.5 V
VIH HIGH Level Input Voltage 2 V
VIL LOW Level Input Voltage 0.8 V
IOH HIGH Level Output Current 0.4 mA
IOL LOW Level Output Current 8 mA
TAFree Air Operating Temperature 0 70 °C
Symbol Parameter Conditions Min Typ Max Units
VIK Input Clamp Voltage VCC = 4.5V, II = 18 mA 1.5 V
VOH HIGH Level IOH = 0.4 mA VCC 2V
Output Voltage VCC = 4.5V to 5.5V
VOL LOW Level VCC = 4.5V IOL = 8 mA 0.35 0.5 V
Output Voltage
IIInput Current @ Max. VCC = 5.5V, VIH = 7V 0.1 mA
Input V oltag e
IIH HIGH Level Input Current VCC = 5.5V, VIH = 2.7V 20 µA
IIL LOW Level Input Current VCC = 5.5V, VIL = 0.4V 0.1 mA
IOOutput Drive Current VCC = 5.5V VO = 2.25V 30 112 mA
ICC Supply Current VCC = 5.5V 5 10 mA
Symbol Parameter Conditions From (Input) Min Max Units
To (Output)
tPLH Propagation Delay Time VCC = 4.5V to 5.5V A, B, C 622ns
LOW-to-HIGH Level Output RL = 500to Y
tPHL Propagation Delay Time CL = 50 pF A, B, C 618ns
HIGH-to-LOW Level Output to Y
tPLH Propagation Delay Time Enable 417ns
LOW-to-HIGH Level Output to Y
tPHL Propagation Delay Time Enable 517ns
HIGH-to-LOW Level Output to Y
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DM74ALS138
Physical Dimensions inches (millimeters) unless otherwise noted
16-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-012, 0.150 Narrow
Package Number M16A
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DM74ALS138
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
16-Lead Small Outline Package (SOP), EIAJ TYPE II, 5.3mm Wide
Package Number M16D
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DM74ALS138 3 to 8 Line Decoder/Demultiplexer
Physical Dimensions inches (millimeters) unless otherwise noted (Continued)
16-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300 Wide
Package Number N16E
Fairchild does no t assume any responsibility for use of any circuitry de scribed, no circuit patent licenses are implied and
Fairchild reserves the right at any time without notice to change said circuitry and specifications.
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FAIRCHILD’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT
DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD
SEMICONDUCTOR CORPORATION. As used herein:
1. Life suppor t de vices o r systems a re devices or syste ms
which, (a) are intended for surgical implant into the
body, or (b) support or sustain life, and (c) whose failure
to perform when properly used in accordance with
instructions for use provided in the labeling, can be rea-
sonably expected to result in a significant injury to the
user.
2. A critical compon ent i n any compon ent of a life su pport
device or system whose failure to perform can be rea-
sonabl y ex pect ed to ca use the fa i lure of the life su pp ort
device or system, or to affect its safety or effectiveness.
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