MM54HC123A MM74HC123A Dual Retriggerable Monostable Multivibrator
January 1988
MM54HC123A MM74HC123A
Dual Retriggerable Monostable Multivibrator
General Description
The MM54 74HC123A high speed monostable multivibra-
tors (one shots) utilize advanced silicon-gate CMOS tech-
nology They feature speeds comparable to low power
Schottky TTL circuitry while retaining the low power and
high noise immunity characteristic of CMOS circuits
Each multivibrator features both a negative A and a posi-
tive B transition triggered input either of which can be
used as an inhibit input Also included is a clear input that
when taken low resets the one shot The 鈥橦C123 can be
triggered on the positive transition of the clear while A is
held low and B is held high
The 鈥橦C123A is retriggerable That is it may be triggered
repeatedly while their outputs are generating a pulse and
the pulse will be extended
Pulse width stability over a wide range of temperature and
supply is achieved using linear CMOS techniques The out-
put pulse equation is simply PW
e
(R
EXT
) (C
EXT
) where PW
is in seconds R is in ohms and C is in farads All inputs are
protected from damage due to static discharge by diodes to
V
CC
and ground
Features
Y
Y
Y
Y
Y
Y
Y
Y
Y
Typical propagation delay 25 ns
Wide power supply range 2V 鈥?6V
Low quiescent current 80
mA
maximum (74HC Series)
Low input current 1
mA
maximum
Fanout of 10 LS-TTL loads
Simple pulse width formula T
e
RC
Wide pulse range 400 ns to
%
(typ)
Part to part variation
g
5% (typ)
Schmitt Trigger A B inputs enable infinite signal input
rise and fall times
Connection Diagram
Dual-In-Line Package
Timing Component
Note
Pin 6 and Pin 14 must be
hard-wired to GND
TL F 5206 鈥?2
TL F 5206 鈥?1
Top View
Order Number MM54HC123A or MM74HC123A
Truth Table
Inputs
Clear
L
X
X
H
H
A
X
H
X
L
B
X
X
L
Q
L
L
L
Outputs
Q
H
H
H
H
e
High Level
L
e
Low Level
u
e
v
e
Transition from Low to High
Transition from High to Low
e
One High Level Pulse
e
One Low Level Pulse
u
H
H
X
e
Irrelevant
v
L
u
C
1995 National Semiconductor Corporation
TL F 5206
RRD-B30M105 Printed in U S A
1
2
3
4
5
6
