HD74LV123A Datasheet, PDF (8/16 Pages) Hitachi Semiconductor – Dual Retriggerable Monostable Multivibrators

HD74LV123A
Timing diagram
t _rr
A
B
CLR
Rext/
Cext
Q
t_w
t_w
t_w +t_rr
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 HD74LV123A
because of the amount of energy stored in the capacitor. When a system containing
this device is powered down, the capacitor may discharge from Vcc through the protection
diodes at pin 7 or pin 15.
Current through the input protection diodes must be limited to 20 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)/
20 mA = 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 HD74LV123A may sustain damage.
To avoid this possibility, use an external calmping diode.
The input pins for unused circuit should be used under conditions to fix the outputs to avoid
malfunction cased by noises. Also, it's recommended that Rext / Cext terminals are open and
external parts are not connected to.
Rev.6.00 Jun. 02, 2004 page 8 of 15