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TC74HC221AP Datasheet(PDF) 4 Page - Toshiba Semiconductor

Part No. TC74HC221AP
Description  Dual Monostable Multivibrator
Download  13 Pages
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Maker  TOSHIBA [Toshiba Semiconductor]
Homepage  http://www.semicon.toshiba.co.jp/eng
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TC74HC221AP Datasheet(HTML) 4 Page - Toshiba Semiconductor

 
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TC74HC221AP/AF/AFN
2007-10-01
4
Timing Chart
Functional Description
(1)
Stand-by state
The external capacitor (Cx) is fully charged to VCC in the stand-by state. That means, before
triggering, the QP and QN transistors which are connected to the Rx/Cx node are in the off state. Two
comparators that relate to the timing of the output pulse, and two reference voltage supplies turn off.
The total supply current is only leakage current.
(2)
Trigger operation
Trigger operation is effective in any of the following three cases. First the condition where the
A
input is low, and the B input has a rising signal; second, where the B input is high, and the A input
has a falling signal; and third, where the A input is low and the B input is high, and the CLR
input has a rising signal.
After a trigger becomes effective, comparators C1 and C2 start operating, and QN is turned on. The
external capacitor discharges through QN. The voltage level at the Rx/Cx node drops. If the Rx/Cx
voltage level falls to the internal reference voltage Vref L, the output of C1 becomes low. The flip-flop
is then reset and QN turns off. At that moment C1 stops but C2 continues operating.
After QN turns off, the voltage at the Rx/Cx node starts rising at a rate determined by the time
constant of external capacitor Cx and resistor Rx.
Upon the triggering, output Q becomes high, following some delay time of the internal F/F and
gates. It stays high even if the voltage of Rx/Cx changes from falling to rising. When Rx/Cx reaches
the internal reference voltage Vref H, the output of C2 becomes low, the output Q goes low and C2
stops its operation. That means, after triggering, when the voltage level of the Rx/Cx node reaches
Vref H, the IC returns to its MONOSTABLE state.
With large values of Cx and Rx, and ignoring the discharge time of the capacitor and internal
delays of the IC, the width of the output pulse, tw (OUT), is as follows:
tw (OUT)
= 1.0 Cx Rx
(3)
Reset operation
In normal operation, CLR input is held high. If CLR is low, a trigger has no effect because the Q
output is held low and trigger control F/F is reset. Also, QP turns on and Cx is charge rapidly to VCC.
This means if CLR input is set low, the IC goes into a wait state.


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