74HC4538DB 데이터 시트보기 (PDF) - Nexperia B.V. All rights reserved
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74HC4538DB Datasheet PDF : 21 Pages
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11 Application information
74HC4538
Dual retriggerable precision monostable multivibrator
11.1 Power-down considerations
A large capacitor (CEXT) 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 VCC 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 (DEXT) preferably a germanium or Schottky type diode able to
withstand large current surges and connect as shown in Figure 10
DEXT
GND
CEXT
REXT
VCC
nCEXT
nREXT/CEXT
Figure 10. Power-down protection circuit
001aak193
11.2 Graphs
1.6
normalized
K factor
(K)
1.2
1 kΩ
2 kΩ
5.6 kΩ
51 kΩ
1 MΩ
1.0
0.8
0.6
10- 10
10- 9
10- 8
10- 7
10- 6
VCC = 4.5 V; Tamb = 25 °C.
Figure 11. Typical pulse width accuracy versus external capacitance
001aak196 1.12
REXT ×
CEXT
(tW)
0.84
0.70
0.56
10- 5
0.42
10- 4
CEXT (F)
74HC4538
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 5 — 17 March 2017
© Nexperia B.V. 2017. All rights reserved.
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