HD74LV221A Datasheet, PDF (10/19 Pages) Hitachi Semiconductor – Dual Monostable Multivibrators

HD74LV221A
Timing diagram
A
B
CLR
Rext/
Cext
Q
Q
t_w
t_w
t_w
Caution in use
In order to prevent any malfunctions due to noise, connect a high frequency performance capacitor
between Vcc and GND, and keep the wiring between the external components and Cext, Rext/Cext
pins as short as possible.
Large values of Cext may cause problems when powering down the HD74LV221A because of the amount
of energy stored in the capacitoe. When a system containing diodes at pin 7 or pin15.
Current through the input protection diodes must be limited to 10 mA; therefore, the turn-off time of the Vcc
power supply must not be faster than t = Vcc • Cext/(20 mA). for example, if Vcc 5 V and Cext = 22 µF,
the Vcc supply must turn off no faster than t = (5 V) • (22 µF)/20mA = 5.5 ms. This is usually not a problem
because power supplies are heavily filtered and cannot discharge at this rate.
When a more rapid decrease of Vcc to zero volts occurs, the HD74LV221A may sustain damage. To avoid
this possibility, use an external calmping diode.
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