tc74hc423ap TOSHIBA Semiconductor CORPORATION, tc74hc423ap Datasheet - Page 4

• Manufacturer Part Number: tc74hc423ap
• Description: Dual Retriggerable Monostable Multivibrator
• Manufacturer: TOSHIBA Semiconductor CORPORATION

Timing Chart
Functional Description
(1)
(2)
(3)
(4)
Stand-by state
triggering, the Q
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.
Trigger operation
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.
external capacitor discharges through Q
voltage level falls to the internal reference voltage Vref L, the output of C1 becomes low. The flip-flop
is then reset and Q
of external capacitor Cx and resistor Rx.
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 reaches Vref H,
the IC returns to its MONOSTABLE state.
delays of the IC, the width of the output pulse, tw (OUT), is as follows:
Retrigger operation
only if the IC is charging Cx. The voltage level of the Rx/Cx node then falls to Vref L level again.
Therefore the Q output stays high if the next trigger comes in before the time period set by Cx and
Rx.
it will have no effect.
Reset operation
output is held low and the trigger control F/F is reset. Also, Q
V
CC
The external capacitor Cx is fully charged to V
Trigger operation is effective in either of the following two cases. First, the condition where the A
After a trigger becomes effective, comparators C1 and C2 start operating, and Q
After Q
Upon the triggering, output Q becomes high, following some delay time of the internal F/F and
With large values of Cx and Rx, and ignoring the discharge time of the capacitor and internal
When a new trigger is applied to input A or B while in the MONOSTABLE state, it is effective
If the 2nd trigger is very close to previous trigger, such as an occurrence during the discharge cycle,
The minimum time for a trigger to be effective 2nd trigger, trr (min), depends on V
In normal operation, CLR input is held high. If CLR is low, a trigger has no effect because the Q
This means if CLR input is set low, the IC goes into a wait state.
tw (OUT) = 1.0 ･ Cx ･ Rx
.
N
turns off, the voltage at the Rx/Cx starts rising at a rate determined by the time constant
P
and Q
N
turns off. At that moment C1 stops but C2 continues operating.
N
transistors which are connected to the Rx/Cx node are in the off state. Two
N
. The voltage level of the Rx/Cx node drops. If the Rx/Cx
4
CC
in the stand-by state. That means, before
P
turns on and Cx is charged rapidly to
TC74HC423AP/AF
N
is turned on. The
CC
2007-10-01
and Cx.