74HC123 Datasheet, PDF (9/17 Pages) NXP Semiconductors – Dual retriggerable monostable multivibrator with reset

Philips Semiconductors
Dual retriggerable monostable
multivibrator with reset
Product specification
74HC/HCT123
Notes to AC characteristics
1. For other R_EXT and C_EXT combinations see Fig.9.
If C_EXT > 10 nF, the next formula is valid:
t_W = K × R_EXT × C_EXT (typ.)
where: t_W = output pulse width in ns;
R_EXT = external resistor in kΩ; C_EXT = external capacitor in pF;
K = constant = 0.55 for V_CC = 5.0 V and 0.48 for V_CC = 2.0 V.
The inherent test jig and pin capacitance at pins 15 and 7 (nR_EXT / C_EXT) is approximately 7 pF.
2. The time to retrigger the monostable multivibrator depends on the values of R_EXT and C_EXT.
The output pulse width will only be extended when the time between the active-going edges of the trigger input pulses
meets the minimum retrigger time.
If C_EXT > 10 pF, the next formula (at V_CC = 5.0 V) for the set-up time of a retrigger pulse is valid:
t_rt = 30 + 0.19 × R_EXT × C_EXT0.9 + 13 × R_EXT1.05 (typ.)
where:
t_rt = retrigger time in ns;
C_EXT = external capacitor in pF;
R_EXT = external resistor in kΩ.
The inherent test jig and pin capacitance at pins 15 and 7 (nR_EXT / C_EXT) is 7 pF.
3. When the device is powered-up, initiate the device via a reset pulse, when C_EXT < 50 pF.
1998 Jul 08
9