74HC423N datasheet(8/14 Pages) PHILIPS

8 / 14 page

1998 Jul 08

Philips Semiconductors

Product speciﬁcation

Dual retriggerable monostable

multivibrator with reset

74HC/HCT423

Notes

1. For other REXT and CEXT combinations see Fig.9.

If CEXT > 10 pF, the next formula is valid:

tW =K × REXT × CEXT (typ.)

where: tW

= output pulse width in ns;

REXT = external resistor in kΩ;CEXT = external capacitor in pF;

= constant = 0.45 for VCC = 5.0 V and 0.55 for VCC = 2.0 V.

The inherent test jig and pin capacitance at pins 15 and 7 (nREXT/CEXT) is approximately 7 pF.

2. The time to retrigger the monostable multivibrator depends on the values of REXT and CEXT.

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 CEXT > 10 pF, the next formula (at VCC = 5.0 V) for the set-up time of a retrigger pulse is valid:

trt =30 + 0.19 × REXT × CEXT0.9 + 13 × REXT1.05 (typ.)

where, trt

= retrigger time in ns;

CEXT = external capacitor in pF;

REXT = external resistor in kΩ.

The inherent test jig and pin capacitance at pins 15 and 7 (nREXT/CEXT) is 7 pF.

3. When the device is powered-up, initiate the device via a reset pulse, when CEXT < 50 pF.

AC WAVEFORMS

Fig.7 Output pulse control using retrigger pulse; nRD = HIGH.

Fig.8 Output pulse control using reset input nRD; nA = LOW.

74HC423N Datasheet(PDF) 8 Page - NXP Semiconductors