Page 1
DATA SH EET
Product specification
File under Integrated Circuits, IC06
December 1990
INTEGRATED CIRCUITS
74HC/HCT238
3-to-8 line decoder/demultiplexer
For a complete data sheet, please also download:
•The IC06 74HC/HCT/HCU/HCMOS Logic Family Specifications
•The IC06 74HC/HCT/HCU/HCMOS Logic Package Information
•The IC06 74HC/HCT/HCU/HCMOS Logic Package Outlines
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December 1990 2
Philips Semiconductors Product specification
3-to-8 line decoder/demultiplexer 74HC/HCT238
FEATURES
• Demultiplexing capability
• Multiple input enable for easy expansion
• Ideal for memory chip select decoding
• Active HIGH mutually exclusive outputs
• Output capability: standard
• ICC category: MSI
GENERAL DESCRIPTION
The 74HC/HCT238 are high-speed Si-gate CMOS devices
and are pin compatible with low power Schottky TTL
(LSTTL). They are specified in compliance with JEDEC
standard no. 7A.
The 74HC/HCT238 decoders accept three binary
weighted address inputs (A
0
, A1, A2) and when enabled,
provide 8 mutually exclusive active HIGH outputs
(Y0 to Y7).
The “238” features three enable inputs: two active LOW
(E1 and E2) and one active HIGH (E3). Every output will be
LOW unless E1 and E2 are LOW and E3 is HIGH.
This multiple enable function allows easy parallel
expansion of the “238” to a 1-of-32 (5 lines to 32 lines)
decoder with just four “238” ICs and one inverter.
The “238” can be used as an eight output demultiplexer by
using one of the active LOW enable inputs as the data
input and the remaining enable inputs as strobes. Unused
enable inputs must be permanently tied to their
appropriate active HIGH or LOW state.
The “238” is identical to the “138” but has non-inverting
outputs.
QUICK REFERENCE DATA
GND = 0 V; T
amb
=25°C; tr=tf= 6 ns
Notes
1. C
PD
is used to determine the dynamic power dissipation (PD in µW):
PD=CPD× V
CC
2
× fi+ ∑ (CL× V
CC
2
× fo) where:
fi= input frequency in MHz
fo= output frequency in MHz
∑ (CL× V
CC
2
× fo) = sum of outputs
CL= output load capacitance in pF
VCC= supply voltage in V
2. For HC the condition is VI= GND to V
CC
For HCT the condition is VI= GND to VCC− 1.5 V
ORDERING INFORMATION
See
“74HC/HCT/HCU/HCMOS Logic Package Information”
.
SYMBOL PARAMETER CONDITIONS
TYPICAL
UNIT
HC HCT
t
PHL/ tPLH
propagation delay CL= 15 pF; VCC=5 V
A
n
to Y
n
14 18 ns
E
3
to Y
n
16 20 ns
En to Y
n
17 21 ns
C
I
input capacitance 3.5 3.5 pF
C
PD
power dissipation capacitance per package notes 1 and 2 72 76 pF
Page 3
December 1990 3
Philips Semiconductors Product specification
3-to-8 line decoder/demultiplexer 74HC/HCT238
PIN DESCRIPTION
PIN NO. SYMBOL NAME AND FUNCTION
1, 2, 3 A
0
to A
2
address inputs
4, 5
E1, E
2
enable inputs (active LOW)
6E
3
enable input (active HIGH)
8 GND ground (0 V)
15, 14, 13, 12, 11, 10, 9, 7 Y
0
to Y
7
outputs (active HIGH)
16 V
CC
positive supply voltage
Fig.1 Pin configuration. Fig.2 Logic symbol.
Fig.3 IEC logic symbol.
(a)
(b)
Page 4
December 1990 4
Philips Semiconductors Product specification
3-to-8 line decoder/demultiplexer 74HC/HCT238
Fig.4 Functional diagram. Fig.5 Logic diagram.
FUNCTION TABLE
Note
1. H = HIGH voltage level
L = LOW voltage level
X = don’t care
INPUTS OUTPUTS
E
1
E
2
E
3
A
0
A
1
A
2
Y
0
Y
1
Y
2
Y
3
Y
4
Y
5
Y
6
Y
7
H
X
X
X
H
X
X
X
L
X
X
X
X
X
X
X
X
X
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
H
H
H
H
L
H
L
H
L
L
H
H
L
L
L
L
H
L
L
L
L
H
L
L
L
L
H
L
L
L
L
H
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
H
H
H
H
L
H
L
H
L
L
H
H
H
H
H
H
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
L
H
L
L
L
L
H
L
L
L
L
H
L
L
L
L
H
Page 5
December 1990 5
Philips Semiconductors Product specification
3-to-8 line decoder/demultiplexer 74HC/HCT238
DC CHARACTERISTICS FOR 74HC
For the DC characteristics see
“74HC/HCT/HCU/HCMOS Logic Family Specifications”
.
Output capability: standard
ICC category: MSI
AC CHARACTERISTICS FOR 74HC
GND = 0 V; t
r=tf
= 6 ns; CL= 50 pF
SYMBOL PARAMETER
T
amb
(°C)
UNIT
TEST CONDITIONS
74HC
V
CC
(V)
WAVEFORMS
+25 −40 to +85 −40 to +125
min. typ. max. min. max. min. max.
t
PHL
/ t
PLH
propagation delay
An to Y
n
47
17
14
150
30
26
190
38
33
225
45
38
ns 2.0
4.5
6.0
Fig.6
t
PHL
/ t
PLH
propagation delay
E3 to Y
n
52
19
15
160
32
27
200
40
34
240
48
41
ns 2.0
4.5
6.0
Fig.6
t
PHL
/ t
PLH
propagation delay
En to Y
n
50
18
14
155
31
26
195
39
33
235
47
40
ns 2.0
4.5
6.0
Fig.7
t
THL
/ t
TLH
output transition time 19
7
6
75
15
13
95
19
16
110
22
19
ns 2.0
4.5
6.0
Figs 6 and 7
Page 6
December 1990 6
Philips Semiconductors Product specification
3-to-8 line decoder/demultiplexer 74HC/HCT238
DC CHARACTERISTICS FOR 74HCT
For the DC characteristics see
“74HC/HCT/HCU/HCMOS Logic Family Specifications”
.
Output capability: standard
ICC category: MSI
Note to HCT types
The value of additional quiescent supply current (∆I
CC
) for a unit load of 1 is given in the family specifications.
To determine ∆ICC per input, multiply this value by the unit load coefficient shown in the table below.
AC CHARACTERISTICS FOR 74HCT
GND = 0 V; t
r=tf
= 6 ns; CL= 50 pF
INPUT UNIT LOAD COEFFICIENT
A
n
E
n
E
3
0.70
0.40
1.45
SYMBOL PARAMETER
T
amb
(°C)
UNIT
TEST CONDITIONS
74HCT
V
CC
(V)
WAVEFORMS
+25 −40 to +85 −40 to +125
min. typ. max. min. max. min. max.
t
PHL
propagation delay
An to Y
n
21 35 44 53 ns 4.5 Fig.6
t
PLH
propagation delay
An to Y
n
17 35 44 53 ns 4.5 Fig.6
t
PHL
propagation delay
E3 to Y
n
22 37 46 56 ns 4.5 Fig.6
t
PLH
propagation delay
E3 to Y
n
18 37 46 56 ns 4.5 Fig.6
t
PHL
propagation delay
En to Y
n
21 35 44 53 ns 4.5 Fig.7
t
PLH
propagation delay
En to Y
n
18 35 44 53 ns 4.5 Fig.7
t
THL
/ t
TLH
output transition time 7 15 19 22 ns 4.5 Figs 6 and 7
Page 7
December 1990 7
Philips Semiconductors Product specification
3-to-8 line decoder/demultiplexer 74HC/HCT238
AC WAVEFORMS
PACKAGE OUTLINES
See
“74HC/HCT/HCU/HCMOS Logic Package Outlines”
.
Fig.6 Waveforms showing the address input (An) and enable input (E3) to output (Yn) propagation delays and
the output transition times.
(1) HC : VM= 50%; VI= GND to VCC.
HCT: V
M
= 1.3 V; VI= GND to 3 V.
Fig.7 Waveforms showing the enable input (En) to output (Yn) propagation delays and the output transition
times.
(1) HC : VM= 50%; VI= GND to VCC.
HCT: V
M
= 1.3 V; VI= GND to 3 V.
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