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74HCT423DB Datasheet(数据表) 2 Page - NXP Semiconductors

部件型号  74HCT423DB
说明  Dual retriggerable monostable multivibrator with reset
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制造商  PHILIPS [NXP Semiconductors]
网页  http://www.nxp.com
标志 

 
 2 page
background image
1998 Jul 08
2
Philips Semiconductors
Product specification
Dual retriggerable monostable
multivibrator with reset
74HC/HCT423
FEATURES
• DC triggered from active HIGH or active LOW inputs
• Retriggerable for very long pulses up to 100% duty
factor
• Direct reset terminates output pulse
• Schmitt-trigger action on all inputs except for the reset
input
• Output capability: standard (except for nREXT/CEXT)
• ICC category: MSI
GENERAL DESCRIPTION
The 74HC/HCT423 are high-speed Si-gate CMOS devices
and are pin compatible with low power Schottky TTL
(LSTTL). They are specified in compliance with JEDEC
standard no. 7A.
The 74HC/HCT423 are dual retriggerable monostable
multivibrators with output pulse width control by two
methods. The basic pulse time is programmed by
selection of an external resistor (REXT) and capacitor
(CEXT). The external resistor and capacitor are normally
connected as shown in Fig.6.
Once triggered, the basic output pulse width may be
extended by retriggering the gated active LOW-going edge
input (nA) or the active HIGH-going edge input (nB). By
repeating this process, the output pulse period
(nQ = HIGH, nQ = LOW) can be made as long as desired.
When nRD is LOW, it forces the nQ output LOW, the
nQ output HIGH and also inhibits the triggering.
Figures 7 and 8 illustrate pulse control by reset. The basic
output pulse width is essentially determined by the values
of the external timing components REXT and CEXT.
For pulse widths, when CEXT < 10 000 pF, see Fig.9.
When CEXT > 10 000 pF, the typical output pulse width is
defined as:
tW = 0.45 × REXT × CEXT (typ.),
where, tW = pulse width in ns;
REXT = external resistor in kΩ;
CEXT = external capacitor in pF.
Schmitt-trigger action in the nA and nB inputs, makes the
circuit highly tolerant to slower input rise and fall times.
The “423” is identical to the “123” but cannot be triggered
via the reset input.
QUICK REFERENCE DATA
GND = 0 V; Tamb = 25 °C; tr = tf = 6 ns
Notes
1. CPD is used to determine the dynamic power dissipation (PD in µW):
PD = CPD × VCC2 × fi +∑ (CL × VCC2 × fo) + 0.75 × CEXT × VCC2 × fo + D × 16 × VCC where:
fi = input frequency in MHz
fo = output frequency in MHz
D = duty factor in %
∑ (CL × VCC2 × fo) = sum of outputs
CL = output load capacitance in pF
VCC = supply voltage in V
CEXT = timing capacitance in pF
2. For HC the condition is VI = GND to VCC
For HCT the condition is VI = GND to VCC − 1.5 V
SYMBOL
PARAMETER
CONDITIONS
TYPICAL
UNIT
HC
HCT
tPHL/ tPLH
propagation delay
CL = 15 pF; VCC = 5 V;
REXT =5 kΩ; CEXT = 0 pF
nA, nB to nQ, nQ25
26
ns
nRD to nQ, nQ20
22
ns
CI
input capacitance
3.5
3.5
pF
tW
minimum output pulse width nQ, nQ
notes 1 and 2
75
75
ns




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