MM74HC123A Dual Retriggerable Monostable Multivibrator
September 1983
Revised May 2001
MM74HC123A
Dual Retriggerable Monostable Multivibrator
General Description
The MM74HC123A high speed monostable multivibrators
(one shots) utilize advanced silicon-gate CMOS technol-
ogy. They feature speeds comparable to low power Schot-
tky 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 MM74HC123A
can be triggered on the positive transition of the clear while
A is held LOW and B is held HIGH.
The MM74HC123A is retriggerable. That is it may be trig-
gered 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
=
(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
s
Typical propagation delay: 25 ns
s
Wide power supply range: 2V–6V
s
Low quiescent current: 80
µ
A maximum (74HC Series)
s
Low input current: 1
µ
A maximum
s
Fanout of 10 LS-TTL loads
s
Simple pulse width formula T
=
RC
s
Wide pulse range: 400 ns to
∞
(typ)
s
Part to part variation:
±
5% (typ)
s
Schmitt Trigger A & B inputs allow rise and fall times to
be as slow as one second
Ordering Code:
Order Number
MM74HC123AM
MM74HC123ASJ
MM74HC123AMTC
MM74HC123AN
Package Number
M16A
M16D
MTC16
N16E
Package Description
16-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-012, 0.150" Narrow
16-Lead Small Outline Package (SOP), EIAJ TYPE II, 5.3mm Wide
16-Lead Thin Shrink Small Outline Package (TSSOP), JEDEC MO-153, 4.4mm Wide
16-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300" Wide
Devices also available in Tape and Reel. Specify by appending the suffix letter “X” to the ordering code.
Connection Diagram
Timing Component
Note:
Pin 6 and Pin 14 must be hard-wired to GND.
Top View
© 2001 Fairchild Semiconductor Corporation
DS005206
www.fairchildsemi.com
MM74HC123A
Truth Table
Inputs
Clear
L
X
X
H
H
A
X
H
X
L
B
X
X
L
Q
L
L
Outputs
Q
H
H
↑
H
H
↓
L
↑
H
L
↑
↓
HIGH Level
LOW Level
Transition from LOW-to-HIGH
Transition from HIGH-to-LOW
=
One HIGH Level Pulse
=
One LOW Level Pulse
X
=
Irrelevant
=
=
=
=
L
H
Logic Diagram
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2
MM74HC123A
Absolute Maximum Ratings
(Note 1)
(Note 2)
Supply Voltage (V
CC
)
DC Input Voltage (V
IN
)
DC Output Voltage (V
OUT
)
Clamp Diode Current (I
IK
, I
OK
)
DC Output Current, per pin (I
OUT
)
DC V
CC
or GND Current, per pin (I
CC
)
Storage Temperature Range (T
STG
)
Power Dissipation (P
D
)
(Note 3)
S.O. Package only
Lead Temperature (T
L
)
(Soldering 10 seconds)
260
°
C
600 mW
500 mW
Recommended Operating
Conditions
Min
Supply Voltage (V
CC
)
DC Input or Output Voltage
(V
IN
, V
OUT
)
Operating Temperature Range (T
A
)
Input Rise or Fall Times
(Clear Input)
(t
r
, t
f
)
V
CC
=
2.0V
V
CC
=
4.5V
V
CC
=
6.0V
1000
500
400
ns
ns
ns
2
0
Max
6
V
CC
Units
V
V
−
0.5V to
+
7.0V
−
1.5V to V
CC
+
1.5V
−
0.5V to V
CC
+
0.5V
±
20 mA
±
25 mA
±
50 mA
−
65
°
C to
+
150
°
C
−
40
+
85
°
C
Note 1:
Maximum Ratings are those values beyond which damage to the
device may occur.
Note 2:
Unless otherwise specified all voltages are referenced to ground.
Note 3:
Power Dissipation Temperature Derating: Plastic “N” Package:
−
12mW/°C from 65°C to 85°C
DC Electrical Characteristics
Symbol
V
IH
Parameter
Minimum HIGH Level Input
Voltage
V
IL
Maximum LOW Level Input
Voltage
V
OH
Minimum HIGH Level
Output Voltage
V
IN
=
V
IH
or V
IL
|I
OUT
|
≤
20
µA
Conditions
(Note 4)
V
CC
2.0V
4.5V
6.0V
2.0V
4.5V
6.0V
2.0V
4.5V
6.0V
2.0
4.5
6.0
4.2
5.7
0
0
0
0.2
0.2
T
A
=
25°C
Typ
1.5
3.15
4.2
0.3
0.9
1.2
1.9
4.4
5.9
3.98
5.48
0.1
0.1
0.1
0.26
0.26
±0.5
±0.1
8.0
36
0.33
0.7
80
1.0
2.0
T
A
= −40
to 85°C T
A
= −55
to 125°C
Guaranteed Limits
1.5
3.15
4.2
0.3
0.9
1.2
1.9
4.4
5.9
3.84
5.34
0.1
0.1
0.1
0.33
0.33
±5.0
±1.0
80
110
1.3
2.6
1.5
3.15
4.2
0.3
0.9
1.2
1.9
4.4
5.9
3.7
5.2
0.1
0.1
0.1
0.4
0.4
±5.0
±1.0
160
130
1.6
3.2
Units
V
V
V
V
V
V
V
V
V
V
4.5V
6.0V
2.0V
4.5V
6.0V
V
V
V
V
V
V
4.5V
6.0V
6.0V
6.0V
6.0V
2.0V
4.5V
6.0V
V
V
µA
µA
µA
µA
mA
mA
V
IN
=
V
IH
or V
IL
|I
OUT
|
≤
4.0 mA
|I
OUT
|
≤
5.2 mA
V
OL
Maximum LOW Level
Output Voltage
V
IN
=
V
IH
or V
IL
|I
OUT
|
≤
20
µA
V
IN
=
V
IH
or V
IL
|I
OUT
|
≤
4 mA
|I
OUT
|
≤
5.2 mA
I
IN
I
IN
I
CC
I
CC
Maximum Input Current
(Pins 7, 15)
Maximum Input Current
(all other pins)
Maximum Quiescent Supply V
IN
=
V
CC
or GND
Current (standby)
Maximum Active Supply
Current (per
monostable)
I
OUT
=
0
µA
V
IN
=
V
CC
or GND
R/C
EXT
=
0.5V
CC
V
IN
=
V
CC
or GND
V
IN
=
V
CC
or GND
Note 4:
For a power supply of 5V
±10%
the worst-case output voltages (V
OH
, V
OL
) occur for HC at 4.5V. Thus the 4.5V values should be used when design-
ing with this supply. Worst-case V
IH
and V
IL
occur at V
CC
=
5.5V and 4.5V respectively. (The V
IH
value at 5.5V is 3.85V.) The worst-case leakage current
(I
IN
, I
CC
, and I
OZ
) occur for CMOS at the higher voltage and so the 6.0V values should be used.
3
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MM74HC123A
AC Electrical Characteristics
V
CC
=
5V, T
A
=
25
°
C, C
L
=
15 pF, t
r
=
t
f
=
6 ns
Symbol
Parameter
t
PLH
t
PHL
t
PHL
t
PLH
t
W
t
REM
t
WQ(MIN)
t
WQ
Maximum Trigger Propagation Delay
A, B or Clear to Q
Maximum Trigger Propagation Delay
A, B or Clear to Q
Maximum Propagation Delay, Clear to Q
Maximum Propagation Delay, Clear to Q
Minimum Pulse Width, A, B or Clear
Minimum Clear Removal Time
Minimum Output Pulse Width
Output Pulse Width
C
EXT
=
28 pF
R
EXT
=
2 kΩ
C
EXT
=
1000 pF
R
EXT
=
10 kΩ
10
µs
400
20
22
14
27
33
26
0
ns
ns
ns
ns
ns
25
42
ns
Conditions
Typ
22
Limit
33
Units
ns
AC Electrical Characteristics
C
L
=
50 pF t
r
=
t
f
=
6 ns (unless otherwise specified)
Symbol
t
PLH
Parameter
Maximum Trigger Propagation
Delay, A, B or Clear to Q
t
PHL
Maximum Trigger Propagation
Delay, A, B or Clear to Q
t
PHL
Maximum Propagation Delay
Clear to Q
t
PLH
Maximum Propagation Delay
Clear to Q
t
W
Minimum Pulse Width
A, B, Clear
t
REM
Minimum Clear
Removal Time
t
TLH
, t
THL
Maximum Output
Rise and Fall Time
t
WQ(MIN)
Minimum Output
Pulse Width
t
WQ
C
IN
C
IN
C
PD
Output Pulse Width
Maximum Input
Capacitance (Pins 7 & 15)
Maximum Input
Capacitance (other inputs)
Power Dissipation
Capacitance
Note 5:
C
PD
determines the no load dynamic power consumption, P
D
=
C
PD
V
CC
2 f
+
I
CC
V
CC
, and the no load dynamic current consumption,
I
S
=
C
PD
V
CC
f
+
I
CC
.
Conditions
V
CC
2.0V
4.5V
6.0V
2.0V
4.5V
6.0V
2.0V
4.5V
6.0V
2.0V
4.5V
6.0V
2.0V
4.5V
6.0V
2.0V
4.5V
6.0V
2.0V
4.5V
6.0V
T
A
=
25°C
Typ
77
26
21
88
29
24
54
23
19
56
25
20
57
17
12
169
42
32
197
48
38
114
34
28
116
36
29
123
30
21
0
0
0
30
8
7
1.5
450
380
1
1
12
6
0.9
1.1
20
10
75
15
13
T
A
= −40
to 85°C T
A
= −55
to 125°C
Guaranteed Limits
194
51
39
229
60
46
132
41
33
135
42
34
144
37
27
0
0
0
95
19
16
210
57
44
250
67
51
143
45
36
147
46
37
157
42
30
0
0
0
110
22
19
Units
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
µs
ns
ns
C
EXT
=
28 pF
R
EXT
=
2 kΩ
R
EXT
=
6 kΩ (V
CC
=
2V)
C
EXT
=
0.1
µF
R
EXT
=
10 kΩ
Min
Mx
a
2.0V
4.5V
6.0V
5.0V
5.0V
0.86
1.14
20
10
0.85
1.15
20
10
ms
ms
pF
pF
pF
(Note 5)
70
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4
MM74HC123A
Theory of Operation
FIGURE 1.
Trigger Operation
As shown in Figure 1 and the logic diagram, before an
input trigger occurs, the one shot is in the quiescent state
with the Q output LOW, and the timing capacitor C
EXT
com-
pletely charged to V
CC
. When the trigger input A goes from
V
CC
to GND (while inputs B and clear are held to V
CC
) a
valid trigger is recognized, which turns on comparator C1
and Nchannel transistor N11. At the same time the output
latch is set. With transistor N1 on, the capacitor C
EXT
rap-
idly discharges toward GND until V
REF1
is reached. At this
point the output of comparator C1 changes state and tran-
sistor N1 turns off. Comparator C1 then turns off while at
the same time comparator C2 turns on. With transistor N1
off, the capacitor C
EXT
begins to charge through the timing
resistor, R
EXT
, toward V
CC
. When the voltage across C
EXT
equals V
REF2
, comparator C2 changes state causing the
output latch to reset (Q goes LOW) while at the same time
disabling comparator C2. This ends the timing cycle with
the monostable in the quiescent state, waiting for the next
trigger.
A valid trigger is also recognized when trigger input B goes
from GND to V
CC
(while input A is at GND and input clear
is at V
CC
2). The MM74HC123A can also be triggered when
clear goes from GND to V
CC
(while A is at GND and B is at
V
CC
6).
It should be noted that in the quiescent state C
EXT
is fully
charged to V
CC
causing the current through resistor R
EXT
to be zero. Both comparators are “off” with the total device
current due only to reverse junction leakages. An added
feature of the MM74HC123A is that the output latch is set
via the input trigger without regard to the capacitor voltage.
Thus, propagation delay from trigger to Q is independent of
the value of C
EXT
, R
EXT
, or the duty cycle of the input
waveform.
Retrigger Operation
The MM74HC123A is retriggered if a valid trigger occurs 3
followed by another trigger 4 before the Q output has
returned to the quiescent (zero) state. Any retrigger, after
the timing node voltage at the R/C
EXT
pin has begun to rise
from V
REF1
, but has not yet reached V
REF2
, will cause an
increase in output pulse width T. When a valid retrigger is
initiated 4, the voltage at the R/C
EXT
pin will again drop to
V
REF1
before progressing along the RC charging curve
toward V
CC
. The Q output will remain HIGH until time T,
after the last valid retrigger.
Because the trigger-control circuit flip-flop resets shortly
after C
X
has discharged to the reference voltage of the
lower reference circuit, the minimum retrigger time, t
rr
is a
function of internal propagation delays and the discharge
time of C
X
:
Another removal/retrigger time occurs when a short clear
pulse is used. Upon receipt of a clear, the one shot must
charge the capacitor up to the upper trip point before the
one shot is ready to receive the next trigger. This time is
dependent on the capacitor used and is approximately:
5
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