IN74HC123
D
UAL
R
ETRIGGERABLE
M
ONOSTABLE
M
ULTIVIBRATOR
The IN74HC123 is identical in pinout to the LS/ALS123. The
device inputs are compatible with standard CMOS outputs; with
pullup resistors, they are compatible with LS/ALSTTL outputs.
There are two trigger inputs,
A
INPUT (negative edge) and
B INPUT (positive edge). These inputs are valid for rising/falling
signals.
The device may also be triggered by using the CLR input
(positive-edge) because of the Schmitt-trigger input; after triggering
the output maintains the MONOSTABLE state for the time period
determined by the external resistor R
X
and capacitor C
X
. Taking
CRL
low breaks this MONOSTABLE STATE. If the next trigger
pulse occurs during the MONOSTABLE period it makes the
MONOSTABLE period longer.
Outputs Directly Interface to CMOS, NMOS, and TTL
Operating Voltage Range: 3.0 to 6.0 V
Low Input Current: 1.0
碌A(chǔ)
High Noise Immunity Characteristic of CMOS Devices
LOGIC DIAGRAM
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ORDERING INFORMATION
IN74HC123N Plastic
IN74HC123D SOIC
T
A
= -55擄 to 125擄 C for all
packages
PIN ASSIGNMENT
PIN 16 =V
CC
PIN 8 = GND
FUNCTION TABLE
Inputs
Outputs
Note
A
B
CRL
Q
Q
H
H
Output
Enable
*
*
X
L
H
L
H
Inhibit
*
*
H
X
H
L
H
Inhibit
L
H
Output
Enable
L
H
Output
Enable
X
X
L
L
H
Inhibit
X = don鈥檛 care
*
- except for monostable period
Note
(1) C
X
, R
X
, D
X
are external components.
(2) D
X
is a clamping diode.
The external capacitor is charged to V
CC
in the
stand-by state, i.e. no trigger. When the supply
voltage is turned off C
X
is discharged mainly
through an internal parasitic diode. If C
X
is
sufficiently large and V
CC
decreases rapidy, there
will be some possibility of damaging the I.C. with
a surge current or latch-up. If the voltage supply
filter capacitor is large enough and V
CC
decrease
slowly, the surge current is automatically limited
and damage the I.C. is avoided. The maximum
forward current of the parasitic diode is
approximately 20 mA.
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3
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