Philips Semiconductors
Product specification
Dual retriggerable monostable multivibrator
with reset
FEATURES
•
ESD protection:
HBM EIA/JESD22-A114-A exceeds 2000 V
MM EIA/JESD22-A115-A exceeds 200 V
CDM EIA/JESD22-C101 exceeds 1000 V
•
All inputs have Schmitt-trigger actions
•
Inputs accept voltages higher than V
CC
•
For AHC only: operates with CMOS input levels
•
For AHCT only: operates with TTL input levels
•
Specified from
−40
to +85
°C
and
−40
to +125
°C
•
DC triggered from active HIGH or active LOW inputs
•
Retriggerable for very long pulses up to 100% duty
factor
•
Direct reset terminates output pulse
•
Output capability: standard (except for nR
EXT
/C
EXT
).
DESCRIPTION
The 74AHC/AHCT123A 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 74AHC/AHCT123A are dual retriggerable monostable
multivibrators with output pulse width control by three
methods. The basic pulse time is programmed by
selection of an external resistor (R
EXT
) and capacitor
(C
EXT
). The external resistor and capacitor are normally
connected as shown in Fig.6.
74AHC123A;
74AHCT123A
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.
Alternatively an output delay can be terminated at any time
by a LOW-going edge on input nR
D
, which also inhibits the
triggering.
An internal connection from nR
D
to the input gate makes it
possible to trigger the circuit by a positive-going signal at
input nR
D
as shown in the function table. Figs 8 and 9
illustrate pulse control by retriggering and early reset. The
basic output pulse width is essentially determined by the
value of the external timing components R
EXT
and C
EXT
.
When C
EXT
≥
10 nF, the typical output pulse width is
defined as: t
W
= R
EXT
×
C
EXT
where t
W
= pulse width in ns;
R
EXT
= external resistor in kΩ; C
EXT
= external capacitor
in pF. Schmitt-trigger action at all inputs makes the circuit
highly tolerant to slower input rise and fall times. The ‘123’
is identical to the ‘423’ but can be triggered via the reset
input.
2000 Mar 15
2
Philips Semiconductors
Product specification
Dual retriggerable monostable multivibrator
with reset
QUICK REFERENCE DATA
GND = 0 V; T
amb
= 25
°C;
t
r
= t
f
≤
3.0 ns.
74AHC123A;
74AHCT123A
TYPICAL
SYMBOL
t
PHL
/t
PLH
PARAMETER
propagation delay
nA, nB to nQ, nQ
nR
D
to nQ, nQ
C
I
C
O
C
PD
Notes
1. C
PD
is used to determine the dynamic power dissipation (P
D
in
µW).
P
D
= C
PD
×
V
CC2
×
f
i
+
∑
(C
L
×
V
CC2
×
f
o
)
×
C
EXT
×
V
CC2
×
f
o
+ D
×
16
×
V
CC
where:
f
i
= input frequency in MHz;
f
o
= output frequency in MHz;
∑
(C
L
×
V
CC2
×
f
o
) = sum of outputs;
D = duty factor in %;
C
L
= output load capacitance in pF;
C
EXT
= timing capacitance in pF;
V
CC
= supply voltage in Volts.
2. The condition is V
I
= GND to V
CC
.
input capacitance
output capacitance
power dissipation capacitance
C
L
= 50 pF; f = 1 MHz; notes 1
and 2
V
I
= V
CC
or GND
CONDITIONS
AHC
C
L
= 15 pF; V
CC
= 5 V;
R
EXT
= 5 kΩ; C
EXT
= 0 pF
5.1
5.6
5
4
57
AHCT
5.0
5.2
3
4
58
ns
ns
pF
pF
pF
UNIT
2000 Mar 15
3
嵌入式系统
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