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74LV123PWDH View Datasheet(PDF) - Philips Electronics

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74LV123PWDH Datasheet PDF : 16 Pages
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Philips Semiconductors
Dual retriggerable monostable multivibrator
with reset
Product specification
74LV123
0.8
‘K’ factor
0.4
APPLICATION INFORMATION
Power-up considerations
When the monostable is powered-up it may produce an output
pulse, with a pulse width defined by the values of RX and CX. This
output pulse can be eliminated using the circuit shown in Figure 6.
nCEXT
CX
RX
VCC
nREXT/CEXT
0
0
1
2
3
4
5
6
VCC (V)
SV00185
Figure 4. HCT typical “k” factor as a function of VCC;
CX = 10 nF; RX = 10 KW to 100 KW.
106
105
104
tW
ns
103
102
REXT =
100kW
50kW
10kW
2kW
0
1
10
102
103
104
CEXT (pF)
SV00141
Figure 5.Typical output pulse width as a function of the
external capacitor values at VCC = 3.3V and Tamb = 25°C.
Q
A
“123”
B
Q
RESET
VCC
SV00152
Figure 6. Power-up output pulse elimination circuit
Power-down considerations
A large capacitor (CX) may cause problems when powering-down
the monostable due to the energy stored in this capacitor. When a
system containing this device is powered-down or a rapid decrease
of VCC to zero occurs, the monostable may sustain damage, due to
the capacitor discharging through the input protection diodes. To
avoid this possibility, connect a damping diode (DX) preferably a
germanium or Schottky type diode able to withstand large current
surges as shown in Figure 7.
DX
VCC
CX
RX
nREXT/CEXT
SV00154
Figure 7. Power-down protection circuit
1998 Apr 28
10
 

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