74vhc221a Fairchild Semiconductor, 74vhc221a Datasheet - Page 2

• Manufacturer Part Number: 74vhc221a
• Description: Dual Non-retriggerable Monostable Multivibrator
• Manufacturer: Fairchild Semiconductor

www.fairchildsemi.com
Truth Table
H
L
X: Don’t Care
Block Diagrams
Note A: Cx, Rx, Dx are external Capacitor, Resistor, and Diode, respectively.
Note B: External clamping diode, Dx;
External capacitor is charged to V
If the supply voltage is turned off, Cx discharges mainly through the internal (parasitic) diode. If Cx is sufficiently large and V
some possibility of damaging the IC through in rush current or latch-up. If the capacitance of the supply voltage filter is large enough and V
the in rush current is automatically limited and damage to the IC is avoided.
The maximum value of forward current through the parasitic diode is
mined as follows:
System Diagram
t
(t
In the event a system does not satisfy the above condition, an external clamping diode (Dx) is needed to protect the IC from rush current.
f
LOW Voltage Level
f
HIGH Voltage Level
is the time between the supply voltage turn off and the supply voltage reaching 0.4 V
(V
CC
0.7) Cx/20 mA


LOW-to-HIGH Transition
HIGH-to-LOW Transition
CC
level in the wait state, i.e. when no trigger is applied.

A
X
H
X
L
L
Inputs

B
H
X
H
X
L
CLR

H
H
H
H
L
20 mA. In the case of a large Cx, the limit of fall time of the supply voltage is deter-
Outputs
Q
L
L
L
2
Q
H
H
H
CC
Output Enable
Inhibit
Inhibit
Output Enable
Output Enable
Reset
)
Function
CC
drops rapidly, there will be
CC
drops slowly,