IN74HC123
DUAL RETRIGGERABLE MONOSTABLE
MULTIVIBRATOR
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,
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 RX and capacitor CX. Taking
ORDERING INFORMATION
IN74HC123N Plastic
IN74HC123D SOIC
TA = -55° to 125° C for all
packages
low breaks this MONOSTABLE STATE. If the next trigger
CRL
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 µA
• High Noise Immunity Characteristic of CMOS Devices
LOGIC DIAGRAM
PIN ASSIGNMENT
PIN 16 =VCC
PIN 8 = GND
FUNCTION TABLE
Inputs
Outputs
Note
A
B
Q
CRL
Q
H
H
Output
Enable
Inhibit
Inhibit
Output
Enable
Output
Enable
Inhibit
Note
(1) CX, RX, DX are external components.
(2) DX is a clamping diode.
X
H
L
L
X
H
H
H
L * H *
L * H *
The external capacitor is charged to VCC in the
stand-by state, i.e. no trigger. When the supply
voltage is turned off CX is discharged mainly
through an internal parasitic diode. If CX is
sufficiently large and VCC 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 VCC 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.
L
H
X
X
L
L
H
X = don’t care
* - except for monostable period
1
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