Philips Semiconductors
Product specification
Dual non-retriggerable monostable
multivibrator with reset
74HC/HCT221
Fig.15 Typical output pulse width as a function of
temperature; CX = 0.1 µF; RX = 10 KΩ;
VCC = 5 V.
Fig.16 k factor as a function of supply voltage;
RX = 10 KΩ; Tamb = 25 °C.
Power-down consideration
PACKAGE OUTLINES
See “74HC/HCT/HCU/HCMOS Logic Package Outlines”.
A large capacitor (CX) 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 VCC 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 (DX)
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.
December 1990
15
NXP [ NXP ]
