HIT HD74HCT138 Datasheet
HD74HCT138
3-to-8-line Decoder/Demultiplexer
Description
The HD74HCT138 has 3 binary select inputs (A, B, and C). If the device is enabled these inputs determine
which one of the eight normally high outputs will go low. Two active low and one active high enables (G1,
G2A and G2B) are provided to ease the cascading of decoders.
Features
• LSTTL Output Logic Level Compatibility as well as CMOS Output Compatibility
• High Speed Operation: tpd (A, B, C to Y) = 18.5 ns typ (CL = 50 pF)
• High Output Current: Fanout of 10 LSTTL Loads
• Wide Operating Voltage: VCC = 4.5 to 5.5 V
• Low Input Current: 1 µA max
• Low Quiescent Supply Current: ICC (static) = 4 µA max (Ta = 25°C)
HD74HCT138
Function Table
Inputs
Enable Select Outputs
G1G
XXHXXXHHHHHHHH
XHXXXXHHHHHHHH
LXXXXXHHHHHHHH
HLLLLLLHHHHHHH
HLLLLHHLHHHHHH
HLLLHLHHLHHHHH
HLLLHHHHHLHHHH
HLLHLLHHHHLHHH
HLLHLHHHHHHLHH
HLLHHLHHHHHHLH
HLLHHHHHHHHHHL
G
2A
CBAY0Y1Y2Y3Y4Y5Y6Y
2B
7
Pin Arrangement
Select
Inputs
Enable
Inputs
Outputs
A
G
2A
G
2B
G
Y
GND
1
2
B
3
C
4
5
6
1
7
7
A
B
C
G
2A
G
2B
G
1
Y
7
Y
0
Y
1
Y
2
Y
3
Y
4
Y
Y
5
6
8
16
15
14
13
12
11
10
V
CC
Y
0
Y
1
Y
2
Y
Outputs
3
Y
4
Y
5
Y
9
6
(Top view)
2
HD74HCT138
DC Characteristics
Ta = –40 to
Ta = 25°C
Item Symbol Min Typ Max Min Max Unit V
Input voltage V
Output voltage V
IH
V
IL
OH
2.0 — — 2.0 — V 4.5 to
— — 0.8 — 0.8 V 4.5 to
4.4 — — 4.4 — V 4.5 Vin = VIH or VILIOH = –20 µA
4.18 — — 4.13 — 4.5 IOH = –4 mA
V
OL
— — 0.1 — 0.1 V 4.5 Vin = VIH or VILIOL = 20 µA
— — 0.26 — 0.33 4.5 IOL = 4 mA
Input current Iin — — ±0.1 — ±1.0 µA 5.5 Vin = VCC or GND
Quiescent supply
I
CC
— — 4.0 — 40 µA 5.5 Vin = VCC or GND, Iout = 0 µA
current
AC Characteristics (CL = 50 pF, Input tr = tf = 6 ns)
+85°C Test Conditions
(V)
CC
5.5
5.5
Ta = –40 to
Ta = 25°C
+85°C Test Conditions
Item Symbol Min Typ Max Min Max Unit V
Propagation delay t
time t
Output rise/fall
time
PHL
PLH
t
PHL
t
PLH
t
PHL
t
PLH
t
TLH
t
THL
— 18 35 — 44 ns 4.5 A, B or C to output
— 19 30 — 38 ns 4.5
— 17 30 — 38 ns 4.5 G1 to output
— 17 30 — 38 ns 4.5
— 17 35 — 44 ns 4.5 G2A or G2B to output
— 17 30 — 38 ns 4.5
— 5 15 — 19 ns 4.5
Input capacitance Cin — 5 10 — 10 pF —
(V)
CC
3
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