Datasheet

1998 Jul 08 9
Philips Semiconductors Product specification
Dual retriggerable monostable
multivibrator with reset
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
EXT
0.9
+13×R
EXT
1.05
(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.