HD74HC423A
Dual Retriggerable Monostable Multivibrators
Description
This multivibrator features output-pulse-duration control by two methods. The basic pulse duration is
programmed by selection of external resistance and capacitance values. Once triggered, the basic pulse
duration may be extended by retriggering the gated low-level-active (A) or high-level-active (B) inputs, or
be reduced by use of the overriding clear. The B input is a Schmitt trigger enabling jitter-free triggering
from input signals with slow transition rates.
Features
High Speed Operation
High Output Current: Fanout of 10 LSTTL Loads
Wide Operating Voltage: V
CC
= 2 to 6 V
Low Input Current: 1 A max
Low Quiescent Supply Current
Function Table
Inputs
Output
Clear
A
B
Q
Q
L
X
X
L
H
X
H
X
L
H
X
X
L
L
H
H
L
H
H
HD74HC423A
4
AC Characteristics (C
L
= 50 pF, Input t
r
= t
f
= 6 ns)
Ta = 25
C
Ta = 40 to
+85
C
Item
Symbol
V
CC
(V) Min Typ Max Min
Max
Unit
Test Conditions
Propagation delay t
PLH
2.0
--
--
210 --
265
ns
A or B to Q
time
4.5
--
20
42
--
53
6.0
--
--
36
--
45
t
PHL
2.0
--
--
240 --
300
ns
A or B to
Q
4.5
--
21
48
--
60
6.0
--
--
41
--
51
t
PHL
2.0
--
--
170 --
215
ns
Clear to Q
4.5
--
17
34
--
43
6.0
--
--
29
--
37
t
PLH
2.0
--
--
180 --
225
ns
Clear to
Q
4.5
--
15
36
--
45
6.0
--
--
31
--
38
Pulse width
t
w
2.0
150 --
--
190
--
ns
A, B, Clear
4.5
30
6
--
38
--
6.0
26
--
--
33
--
Removal time
t
rem
2.0
0
--
--
5
--
ns
Clear
4.5
0
3
--
5
--
6.0
0
--
--
5
--
Minimum output
t
WQ (min)
2.0
--
1.5
--
--
--
s
Cext = 28 pF
Rext = 6 k
pulse width
4.5
--
450 --
--
--
ns
Rext = 2 k
6.0
--
380 --
--
--
Output pulse width t
WQ
4.5
--
1.0
--
--
--
ms
Cext = 0.1
F, Rext = 10 k
Output rise/fall
t
TLH
2.0
--
--
75
--
95
ns
time
t
THL
4.5
--
5
15
--
19
6.0
--
--
13
--
16
Input capacitance
Cin
--
--
--
20
--
20
pF
Pins 7 & 15
--
--
5
10
--
10
Other pins
Caution in use: In order to prevent any malfunctions due to noise, connect a highfrequency performance
capacitor between V
CC
and GND, and keep the wiring between the external components and
Cext, Rext/Cext pins as short as possible.