NXP Semiconductors
12.1.3 Reset timing
74LV123
Dual retriggerable monostable multivibrator with reset
nB input
nRD input
nQ output
tW
nA = LOW
Fig 13. Output pulse control using reset input nRD
tW
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12.2 Power considerations
12.2.1 Power-up
When the monostable multivibrator is powered-up, it may produce an output pulse with a
pulse width defined by the values of REXT and CEXT. This output pulse can be eliminated
using the RC circuit on pin nRD shown in Figure 14.
12.2.2 Power-down
A large capacitor (CEXT) 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 DEXT (preferably a germanium or Schottky type
diode) able to withstand large current surges - see Figure 14.
74LV123
Product data sheet
DEXT
CEXT
REXT
VCC
GND
nCEXT nREXT/CEXT
8
14 (6)
15 (7)
74LV123
1 (9)
nA
nB
2 (10)
13 (5)
nQ
4 (12)
nQ
3 (11)
nRD
RESET
VCC
Fig 14. Power-up and power-down circuit
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All information provided in this document is subject to legal disclaimers.
Rev. 7 — 12 December 2011
© NXP B.V. 2011. All rights reserved.
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