December 1990 15
Philips Semiconductors Product specification
Dual non-retriggerable monostable
multivibrator with reset
74HC/HCT221
Fig.15 Typical output pulse width as a function of
temperature; C
X
= 0.1 µF; R
X
=10KΩ;
V
CC
=5V.
Fig.16 k factor as a function of supply voltage;
R
X
=10KΩ;T
amb
=25°C.
Power-down consideration
A large capacitor (C
X
) may cause problems when
powering-down the monostable due to the energy stored
in this capacitor. When a system containing this device is
powered-down or a rapid decrease of V
CC
to zero occurs,
the monostable may substain damage, due to the
capacitor discharging through the input protection diodes.
To avoid this possibility, use a damping diode (D
X
)
preferably a germanium or Schottky type diode able to
withstand large current surges and connect as shown in
Fig.17.
Fig.17 Power-down protection circuit.
PACKAGE OUTLINES
See
“74HC/HCT/HCU/HCMOS Logic Package Outlines”
.
