74HC_HCT423 All information provided in this document is subject to legal disclaimers. © NXP B.V. 2011. All rights reserved.
Product data sheet Rev. 6 — 19 December 2011 14 of 24
NXP Semiconductors
74HC423; 74HCT423
Dual retriggerable monostable multivibrator with reset
12. Application information
12.1 Timing component connections
The basic output pulse width is essentially determined by the values of the external timing
components R
EXT
and C
EXT
.
12.1.1 Minimum monostable pulse width
To set the minimum pulse width, when C
EXT
< 10 nF, see Figure 8 and
when C
EXT
> 10 nF, the output pulse width is defined as:
t
W
= 0.45 R
EXT
C
EXT
(typ.), where:
t
W
= pulse width in s;
R
EXT
= external resistor in k;
C
EXT
= external capacitor in nF.
12.2 Power-up considerations
When the monostable is powered-up it may produce an output pulse, with a pulse width
defined by the values of R
EXT
and C
EXT
, this output pulse can be eliminated using the
circuit shown in Figure 14
.
(1) For minimum noise generation it is recommended that the nCEXT pins (6, 14) are connected to ground externally to
the GND pin (8).
Fig 13. Timing component connections
001aah917
C
EXT
R
EXT
nA
nB
V
CC
nCEXT
nRD
nREXT/CEXT
nQ
nQ
GND
423
13 (5)
4 (12)
15 (7)14 (6)
3 (11)
8
1 (9)
2 (10)
(1)
