DATA SHEET
Product specification
Supersedes data of December 1990
File under Integrated Circuits, IC06
1998 Jul 08
INTEGRATED CIRCUITS
74HC/HCT423
Dual retriggerable monostable
multivibrator with reset
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
1998 Jul 08
2
Philips Semiconductors
Product specification
Dual retriggerable monostable
multivibrator with reset
74HC/HCT423
FEATURES
DC triggered from active HIGH or active LOW inputs
Retriggerable for very long pulses up to 100% duty
factor
Direct reset terminates output pulse
Schmitt-trigger action on all inputs except for the reset
input
Output capability: standard (except for nR
EXT
/C
EXT
)
I
CC
category: MSI
GENERAL DESCRIPTION
The 74HC/HCT423 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/HCT423 are dual retriggerable monostable
multivibrators with output pulse width control by two
methods. The basic pulse time is programmed by
selection of an external resistor (R
EXT
) and capacitor
(C
EXT
). The external resistor and capacitor are normally
connected as shown in Fig.6.
Once triggered, the basic output pulse width may be
extended by retriggering the gated active LOW-going edge
input (nA) or the active HIGH-going edge input (nB). By
repeating this process, the output pulse period
(nQ = HIGH, nQ = LOW) can be made as long as desired.
When nR
D
is LOW, it forces the nQ output LOW, the
nQ output HIGH and also inhibits the triggering.
Figures 7 and 8 illustrate pulse control by reset. The basic
output pulse width is essentially determined by the values
of the external timing components R
EXT
and C
EXT
.
For pulse widths, when C
EXT
<
10 000 pF, see Fig.9.
When C
EXT
>
10 000 pF, the typical output pulse width is
defined as:
t
W
= 0.45
R
EXT
C
EXT
(typ.),
where, t
W
= pulse width in ns;
R
EXT
= external resistor in k
;
C
EXT
= external capacitor in pF.
Schmitt-trigger action in the nA and nB inputs, makes the
circuit highly tolerant to slower input rise and fall times.
The "423" is identical to the "123" but cannot be triggered
via the reset input.
QUICK REFERENCE DATA
GND = 0 V; T
amb
= 25
C; t
r
= t
f
= 6 ns
Notes
1. C
PD
is used to determine the dynamic power dissipation (P
D
in
W):
P
D
= C
PD
V
CC
2
f
i
+
(C
L
V
CC
2
f
o
)
+
0.75
C
EXT
V
CC
2
f
o
+
D
16
V
CC
where:
f
i
= input frequency in MHz
f
o
= output frequency in MHz
D = duty factor in %
(C
L
V
CC
2
f
o
) = sum of outputs
C
L
= output load capacitance in pF
V
CC
= supply voltage in V
C
EXT
= timing capacitance in pF
2. For HC the condition is V
I
= GND to V
CC
For HCT the condition is V
I
= GND to V
CC
-
1.5 V
SYMBOL
PARAMETER
CONDITIONS
TYPICAL
UNIT
HC
HCT
t
PHL
/ t
PLH
propagation delay
C
L
= 15 pF; V
CC
= 5 V;
R
EXT
= 5 k
; C
EXT
= 0 pF
nA, nB to nQ, nQ
25
26
ns
nR
D
to nQ, nQ
20
22
ns
C
I
input capacitance
3.5
3.5
pF
t
W
minimum output pulse width nQ, nQ
notes 1 and 2
75
75
ns
1998 Jul 08
3
Philips Semiconductors
Product specification
Dual retriggerable monostable
multivibrator with reset
74HC/HCT423
ORDERING INFORMATION
PIN DESCRIPTION
TYPE
NUMBER
PACKAGE
NAME
DESCRIPTION
VERSION
74HC423N;
74HCT423N
DIP16
plastic dual in-line package; 16 leads (300 mil); long body
SOT38-1
74HC423D;
74HCT423D
SO16
plastic small outline package; 16 leads; body width 3.9 mm;
low stand-off height
SOT109-1
PIN NO.
SYMBOL
NAME AND FUNCTION
1, 9
1A, 2A
trigger inputs (negative-edge triggered)
2, 10
1B, 2B
trigger inputs (positive-edge triggered)
3, 11
1R
D
, 2R
D
direct reset action (active LOW)
4, 12
1Q, 2Q
outputs (active LOW)
7
2R
EXT
/C
EXT
external resistor/capacitor connection
8
GND
ground (0 V)
13, 5
1Q, 2Q
outputs (active HIGH)
14, 6
1C
EXT
, 2C
EXT
external capacitor connection
15
1R
EXT
/C
EXT
external resistor/capacitor connection
16
V
CC
positive supply voltage
Fig.1 Pin configuration.
Fig.2
Fig.3 IEC logic symbol.
1998 Jul 08
4
Philips Semiconductors
Product specification
Dual retriggerable monostable
multivibrator with reset
74HC/HCT423
FUNCTION TABLE
Notes
1. H = HIGH voltage level
L = LOW voltage level
X = don't care
= LOW-to-HIGH transition
= HIGH-to-LOW transition
= one HIGH level output pulse
= one LOW level output pulse
2. If the monostable was triggered before this condition was established, the pulse will continue as programmed.
INPUTS
OUTPUTS
nR
D
nA
nB
nQ
nQ
L
X
X
L
H
X
H
X
L
(2)
H
(2)
X
X
L
L
(2)
H
(2)
H
L
H
H
Fig.4 Functional diagram.
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