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PDF HD74LV123A Data sheet ( Hoja de datos )
| Número de pieza | HD74LV123A | |
| Descripción | Dual Retriggerable Monostable Multivibrators | |
| Fabricantes | Hitachi Semiconductor | |
| Logotipo |  |
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HD74LV123A
Dual Retriggerable Monostable Multivibrators
ADE-205-258A (Z)
2nd Edition
June 1999
Description
The HD74LV123A features output pulse-duration control by three methods. In the first method, the A
input is low and the B input goes high. In the second method, the B input is high and the A input goes low.
In the third method, the A input is low, the B input is high, and the clear (CLR) input goes high.
The basic pulse duration is programmed by selecting external resistance and capacitance values.
The external timing capacitor must be connected between Cext and Rext/Cext (positive) and an external
resistor connected between Rext/Cext and Vcc
To obtain variable pulse durations, connect an external variable resistance between Rext/Cext and Vcc.
Once triggered, the basic pulse duration can be extended by retriggering the gated low-level-active (A) or
high-level-active (B) input. Pulse duration can be reduced by taking CLR low.
Features
• VCC = 2.0 V to 5.5 V operation
• All inputs VIH (Max.) = 5.5 V (@VCC = 0 V to 5.5 V)
• All outputs VO (Max.) = 5.5 V (@VCC = 0 V)
• Output current ±6 mA (@VCC = 3.0 V to 3.6 V), ±12 mA (@VCC = 4.5 V to 5.5 V)
1 page  
Logic Diagram
A
B
CLR
HD74LV123A
Rext/
Cext Cext
Q
Q
Q
CLR
Q
5
5 Page 
Timing diagram
A
B
CLR
Rext/
Cext
Q
Q
tw
HD74LV123A
t rr
tw tw +trr
Caution in use
In order to prevent any malfunctions due to noise, connect a high frequency
performance capacitor between Vcc and GND, and keep the wiring between the
External components and Cext, Rext/Cext pins as short as possible.
Large values of Cext may cause problems when powering down the HD74LV123A
because of the amount of energy stored in the capacitor. When a system containing
this device is powered down, the capacitor may discharge from Vcc through the protection
diodes at pin 7 or pin 15.
Current through the input protection diodes must be limited to 20 mA; therefore, the turn-off
time of the Vcc power supply must not be faster than t = Vcc • Cext/(20 mA). For example,
if Vcc = 5 V and Cext = 22 µF, the Vcc supply must turn off no faster than t = (5 V) • (22 µF)/
20 mA = 5.5 ms. This is usually not a problem because power supplies are heavily filtered
and cannot discharge at this rate.
When a more rapid decrease of Vcc to zero volts occurs, the HD74LV123A may sustain damage.
To avoid this possibility, use an external calmping diode.
11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet HD74LV123A.PDF ] | |
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