Nexperia
74HC4538
Dual retriggerable precision monostable multivibrator
74HC4538 All information provided in this document is subject to legal disclaimers. © Nexperia B.V. 2017. All rights reserved.
Product data sheet Rev. 5 — 17 March 2017
12 / 21
11 Application information
11.1 Power-down considerations
A large capacitor (C
EXT
) may cause problems when powering-down the monostable due
to energy stored in this capacitor. When a system containing this device is powered-
down or rapid decrease of V
CC
to zero occurs, the monostable may sustain damage, due
to the capacitor discharging through the input protection diodes. To avoid this possibility,
use a damping diode (D
EXT
) preferably a germanium or Schottky type diode able to
withstand large current surges and connect as shown in Figure 10
001aak193
nREXT/CEXTnCEXT
GND
V
CC
R
EXT
D
EXT
C
EXT
Figure 10. Power-down protection circuit
11.2 Graphs
001aak196
C
EXT
(F)
10
- 10
10
- 5
10
- 4
10
- 6
10
- 7
10
- 9
10
- 8
1.0
1.2
0.8
1.6
0.6
normalized
K factor
(K)
0.70
0.84
0.56
1.12
0.42
R
EXT
×
C
EXT
(t
W
)
1 kΩ
2 kΩ
5.6 kΩ
51 kΩ
1 MΩ
V
CC
= 4.5 V; T
amb
= 25 °C.
Figure 11. Typical pulse width accuracy versus external capacitance
