參數(shù)資料
型號： 74VHC123A
廠商： Fairchild Semiconductor Corporation
英文描述： Automotive Catalog Dual D-Type Positive-Edge-Triggered Flip-Flops With Clear and Preset 14-SOIC -40 to 125
中文描述： 雙Retriggerable單穩(wěn)態(tài)觸發(fā)器
文件頁數(shù)： 2/9頁
文件大?。?/td> 107K
代理商： 74VHC123A
www.fairchildsemi.com
2
7
4
VH
C12
3
A
Pin Descriptions
Truth Table
H
= HIGH Voltage Level
= HIGH-to-LOW Transition
L
= LOW Voltage Level
= LOW-to-HIGH Transition
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 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
Pin Names
Description
A
Trigger Inputs (Negative Edge)
B
Trigger Inputs (Positive Edge)
CLR
Reset Inputs
Cx
External Capacitor
Rx
External Resistor
Q, Q
Outputs
Inputs
Outputs
Function
A
BCLR
QQ
HH