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74VHC123AM View Datasheet(PDF) - Fairchild Semiconductor

Part Name
Description
View to exact match
74VHC123AM
Fairchild
Fairchild Semiconductor Fairchild
74VHC123AM Datasheet PDF : 9 Pages
1 2 3 4 5 6 7 8 9
Pin Descriptions
Pin Names
Description
A
Trigger Inputs (Negative Edge)
B
Trigger Inputs (Positive Edge)
CLR
Reset Inputs
Cx
Rx
Q, Q
External Capacitor
External Resistor
Outputs
Block Diagrams
Truth Table
Inputs
Outputs
Function
A
B
H
CLR
H
Q
Q
Output Enable
XL
H
L H Inhibit
H
L
L
X
H
H
H
L
H
Inhibit
Output Enable
Output Enable
XX
L
H = HIGH Voltage Level
L = LOW Voltage Level
X = Don’t Care
L H Reset
 = HIGH-to-LOW Transition
 = LOW-to-HIGH Transition
Note A: Cx, Rx, Dx are external Capacitor, Resistor, and Diode, respectively.
Note B: External clamping diode, Dx;
External capacitor is charged to VCC level in the wait state, i.e. when no trigger is applied.
If the supply voltage is turned off, Cx discharges mainly through the internal (parasitic) diode. If Cx is sufficiently large and VCC drops rapidly, there will be
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 VCC drops slowly,
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 ±20 mA. In the case of a large Cx, the limit of fall time of the supply voltage is deter-
mined as follows:
tf (VCC 0.7) Cx/20 mA
(tf is the time between the supply voltage turn off and the supply voltage reaching 0.4 VCC)
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.
System Diagram
www.fairchildsemi.com
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