HD74AC538
1-of-8 Decoder with 3-State Output
Description
The HD74AC538 decoder/demultiplexer accepts three Address (A0 to A2) input signal and decodes them
to select one of eight mutually exclusive outputs. A polarity control input (P) determines whether the
outputs are active LOW or active HIGH. A HIGH signal on either of the active LOW output Enable (OE)
inputs forces all outputs to the high impedance state. Two active HIGH and two active LOW input enables
are available for easy expansion to 1-of-32 decoding with four packages, or for data demultiplexing to 1-of-
8 or 1-of-16 destinations.
Features
•
Output Polarity Control
•
Data Demultiplexing Capability
•
Multiple Enables for Expansion
•
Outputs Source/Sink 24 mA
HD74AC538
Pin Names
A
0
to A
2
Address Inputs
E
1
, E
2
E
3
, E
4
P
Enable Inputs (Active LOW)
Enable Inputs (Active HIGH)
Polarity Control Input
OE
1
,
OE
2
Output Enable Inputs (Active LOW)
O
0
to O
7
3-State Outputs
Logic Diagram
A
2
A
1
A
0
E
1
E
2
E
3
E
4
P
OE
1
OE
2
O
0
O
1
O
2
O
3
O
4
O
5
O
6
O
7
3
HD74AC538
Truth Table
Inputs
Function
High impedance
OE
1
OE
2
E
1
H
Z
Disable
L
L
L
L
Active HIGH output
(P = L)
L
L
L
L
L
L
L
L
Active LOW output
(P = L)
L
L
L
L
L
L
L
L
H
L
X
Z
:
:
:
:
High Voltage Level
Low Voltage Level
Immaterial
High Impedance
X
H
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
X
X
H
X
X
X
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
E
2
X
X
X
H
X
X
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
E
3
X
X
X
X
L
X
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
E
4
X
X
X
X
X
L
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
A
2
X
X
X
X
X
X
L
L
L
L
H
H
H
H
L
L
L
L
H
H
H
H
A
1
X
X
X
X
X
X
L
L
H
H
L
L
H
H
L
L
H
H
L
L
H
H
A
0
X
X
X
X
X
X
L
H
L
H
L
H
L
H
L
H
L
H
L
H
L
H
H
L
L
L
L
L
L
L
L
H
H
H
H
H
H
H
L
H
L
L
L
L
L
L
H
L
H
H
H
H
H
H
L
L
H
L
L
L
L
L
H
H
L
H
H
H
H
H
L
L
L
H
L
L
L
L
H
H
H
L
H
H
H
H
L
L
L
L
H
L
L
L
H
H
H
H
L
H
H
H
L
L
L
L
L
H
L
L
H
H
H
H
H
L
H
H
L
L
L
L
L
L
H
L
H
H
H
H
H
H
L
H
L
L
L
L
L
L
L
H
H
H
H
H
H
H
H
L
Outputs
O
0
X
Z
O
1
Z
Z
O
2
Z
Z
O
3
Z
Z
O
4
Z
Z
O
5
Z
Z
O
6
Z
Z
O
7
Z
Z
Outputs equal input
DC Characteristics
(unless otherwise specified)
Item
Maximum quiescent supply current
Maximum quiescent supply current
Symbol
I
CC
I
CC
Max
80
8.0
Unit
µA
µA
Condition
V
IN
= V
CC
or ground, V
CC
= 5.5 V,
Ta = Worst case
V
IN
= V
CC
or ground, V
CC
= 5.5 V,
Ta = 25°C
4
HD74AC538
AC Characteristics: HD74AC538
Ta = +25°C
C
L
= 50 pF
Item
Propagation delay
A
n
to O
n
Propagation delay
A
n
to O
n
Propagation delay
E
1
, or
E
2
to O
n
Propagation delay
E
1
, or
E
2
to O
n
Propagation delay
E
3
, or
E
4
to O
n
Propagation delay
E
3
, or
E
4
to O
n
Propagation delay
P to O
n
Propagation delay
P to O
n
Propagation delay
OE
n
to O
n
Propagation delay
OE
n
to O
n
Propagation delay
OE
n
to O
n
Propagation delay
OE
n
to O
n
Note:
t
PLZ
t
PHZ
t
PZL
t
PZH
t
PHL
t
PLH
t
PHL
t
PLH
t
PHL
t
PLH
t
PHL
Symbol
t
PLH
V
CC
(V)*
1
3.3
5.0
3.3
5.0
3.3
5.0
3.3
5.0
3.3
5.0
3.3
5.0
3.3
5.0
3.3
5.0
3.3
5.0
3.3
5.0
3.3
5.0
3.3
5.0
Min
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
Typ
10.5
8.0
9.5
7.0
11.0
8.0
10.0
8.0
11.0
8.5
10.5
8.0
10.5
9.0
9.0
7.5
7.0
5.0
8.5
5.5
7.0
6.0
9.0
7.0
Max
17.5
12.5
17.5
12.0
19.5
14.5
19.5
14.0
19.5
14.5
20.0
15.0
15.5
11.0
15.0
10.5
14.0
8.5
16.5
9.5
14.0
10.5
14.5
10.5
Ta = –40°C to +85°C
C
L
= 50 pF
Min
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
Max
20.0
14.0
20.0
14.0
23.0
16.5
23.0
16.5
23.0
17.0
23.5
18.0
17.5
12.5
17.0
11.5
15.5
9.5
19.0
11.5
15.5
11.5
17.0
12.0
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
Unit
ns
1. Voltage Range 3.3 is 3.3 V
±
0.3 V
Voltage Range 5.0 is 5.0 V
±
0.5 V
Capacitance
Item
Input capacitance
Power dissipation capacitance
Symbol
C
IN
C
PD
Typ
4.5
100
Unit
pF
pF
Condition
V
CC
= 5.5 V
V
CC
= 5.0 V
5
Microcontroller MCU
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