SN74LS122 SN74LS123
Retriggerable Monostable
Multivibrators
These dc triggered multivibrators feature pulse width control by
three methods. The basic pulse width is programmed by selection of
external resistance and capacitance values. The LS122 has an internal
timing resistor that allows the circuits to be used with only an external
capacitor. Once triggered, the basic pulse width may be extended by
retriggering the gated low-level-active (A) or high-level-active (B)
inputs, or be reduced by use of the overriding clear.
•
Overriding Clear Terminates Output Pulse
•
Compensated for V
CC
and Temperature Variations
•
DC Triggered from Active-High or Active-Low Gated Logic Inputs
•
Retriggerable for Very Long Output Pulses, up to 100% Duty Cycle
•
Internal Timing Resistors on LS122
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14
1
PLASTIC
N SUFFIX
CASE 646
GUARANTEED OPERATING RANGES
Symbol
V
CC
T
A
I
OH
I
OL
R
ext
C
ext
R
ext
/C
ext
Parameter
Supply Voltage
Operating Ambient
Temperature Range
Output Current – High
Output Current – Low
External Timing Resistance
External Capacitance
Wiring Capacitance at
R
ext
/C
ext
Terminal
5.0
Min
4.75
0
Typ
5.0
25
Max
5.25
70
– 0.4
8.0
260
No Restriction
50
pF
Unit
V
°C
mA
mA
k
W
16
1
14
1
SOIC
D SUFFIX
CASE 751A
PLASTIC
N SUFFIX
CASE 648
16
1
SOIC
D SUFFIX
CASE 751B
ORDERING INFORMATION
Device
SN74LS122N
SN74LS122D
SN74LS123N
SN74LS123D
Package
14 Pin DIP
14 Pin
16 Pin DIP
16 Pin
Shipping
2000 Units/Box
2500/Tape & Reel
2000 Units/Box
2500/Tape & Reel
©
Semiconductor Components Industries, LLC, 1999
1
December, 1999 – Rev. 6
Publication Order Number:
SN74LS122/D
SN74LS122 SN74LS123
LS122 FUNCTIONAL TABLE
INPUTS
CLEAR
L
X
X
X
H
H
H
H
H
H
H
↑
↑
A1
X
H
X
X
L
L
X
X
H
↓
↓
L
X
A2
X
H
X
X
X
X
L
L
↓
↓
H
X
L
B1
X
X
L
X
↑
H
↑
H
H
H
H
H
H
B2
X
X
X
L
H
↑
H
↑
H
H
H
H
H
OUTPUTS
Q
L
L
L
L
Q
H
H
H
H
CLEAR
L
X
X
H
H
↑
LS123 FUNCTIONAL TABLE
INPUTS
A
X
H
X
L
↓
L
B
X
X
L
↑
H
H
OUTPUTS
Q
L
L
L
Q
H
H
H
TYPICAL APPLICATION DATA
The output pulse t
W
is a function of the external
components, C
ext
and R
ext
or C
ext
and R
int
on the LS122.
For values of C
ext
≥
1000 pF, the output pulse at V
CC
= 5.0
V and V
RC
= 5.0 V (see Figures 1, 2, and 3) is given by
t
W
= K R
ext
C
ext
where K is nominally 0.45
If C
ext
is on pF and R
ext
is in kΩ then t
W
is in nanoseconds.
The C
ext
terminal of the LS122 and LS123 is an internal
connection to ground, however for the best system
performance C
ext
should be hard-wired to ground.
Care should be taken to keep R
ext
and C
ext
as close to the
monostable as possible with a minimum amount of
inductance between the R
ext
/C
ext
junction and the R
ext
/C
ext
pin. Good groundplane and adequate bypassing should be
designed into the system for optimum performance to ensure
that no false triggering occurs.
It should be noted that the C
ext
pin is internally connected
to ground on the LS122 and LS123, but not on the LS221.
Therefore, if C
ext
is hard-wired externally to ground,
substitution of a LS221 onto a LS123 socket will cause the
LS221 to become non-functional.
The switching diode is not needed for electrolytic
capacitance application and should not be used on the LS122
and LS123.
To find the value of K for C
ext
≥
1000 pF, refer to Figure 4.
Variations on V
CC
or V
RC
can cause the value of K to
change, as can the temperature of the LS123, LS122.
Figures 5 and 6 show the behavior of the circuit shown in
Figures 1 and 2 if separate power supplies are used for V
CC
and V
RC
. If V
CC
is tied to V
RC
, Figure 7 shows how K will
vary with V
CC
and temperature. Remember, the changes in
R
ext
and C
ext
with temperature are not calculated and
included in the graph.
As long as C
ext
≥
1000 pF and 5K
≤
R
ext
≤
260K, the
change in K with respect to R
ext
is negligible.
If C
ext
≤
1000 pF the graph shown on Figure 8 can be used
to determine the output pulse width. Figure 9 shows how K
will change for C
ext
≤
1000 pF if V
CC
and V
RC
are connected
to the same power supply. The pulse width t
W
in
nanoseconds is approximated by
t
W
= 6 + 0.05 C
ext
(pF) + 0.45 R
ext
(kΩ) C
ext
+ 11.6 R
ext
In order to trim the output pulse width, it is necessary to
include a variable resistor between V
CC
and the R
ext
/C
ext
pin
or between V
CC
and the R
ext
pin of the LS122. Figure 10, 11,
and 12 show how this can be done. R
ext
remote should be
kept as close to the monostable as possible.
Retriggering of the part, as shown in Figure 3, must not
occur before C
ext
is discharged or the retrigger pulse will not
have any effect. The discharge time of C
ext
in nanoseconds
is guaranteed to be less than 0.22 C
ext
(pF) and is typically
0.05 C
ext
(pF).
For the smallest possible deviation in output pulse widths
from various devices, it is suggested that C
ext
be kept
≥
1000 pF.
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SN74LS122 SN74LS123
DC CHARACTERISTICS OVER OPERATING TEMPERATURE RANGE
(unless otherwise specified)
Limits
Symbol
V
IH
V
IL
V
IK
V
OH
Parameter
Input HIGH Voltage
Input LOW Voltage
Input Clamp Diode Voltage
Output HIGH Voltage
2.7
– 0.65
3.5
0.25
V
O
OL
Output LOW Voltage
0.35
I
IH
I
IL
I
OS
I
CC
Input HIGH Current
0.1
Input LOW Current
Short Circuit Current (Note 1)
LS122
Power Supply Current
LS123
20
– 20
– 0.4
–100
11
mA
V
CC
= MAX
0.5
20
V
µA
mA
mA
mA
I
OL
= 8.0 mA
0.4
Min
2.0
0.8
– 1.5
Typ
Max
Unit
V
V
V
V
V
Test Conditions
Guaranteed Input HIGH Voltage for
All Inputs
Guaranteed Input LOW Voltage for
All Inputs
V
CC
= MIN, I
IN
= – 18 mA
V
CC
= MIN, I
OH
= MAX, V
IN
= V
IH
or V
IL
per Truth Table
I
OL
= 4.0 mA
V
CC
= V
CC
MIN,
V
IN
= V
IL
or V
IH
per Truth Table
V
CC
= MAX, V
IN
= 2.7 V
V
CC
= MAX, V
IN
= 7.0 V
V
CC
= MAX, V
IN
= 0.4 V
V
CC
= MAX
Note 1: Not more than one output should be shorted at a time, nor for more than 1 second.
AC CHARACTERISTICS
(T
A
= 25°C, V
CC
= 5.0 V)
Limits
Symbol
t
PLH
t
PHL
t
PLH
t
PHL
t
PLH
t
PHL
t
W min
t
W
Q
Parameter
Propagation Delay, A to Q
g
y
Propagation Delay, A to Q
Propagation Delay, B to Q
g
y
Propagation Delay, B to Q
Propagation Delay, Clear to Q
g
y
Propagation Delay, Clear to Q
A or B to Q
A to B to Q
4.0
Min
Typ
23
32
23
34
28
20
116
4.5
Max
33
ns
45
44
ns
56
45
ns
27
200
5.0
ns
µs
C
ext
= 1000 pF, R
ext
= 10 kΩ,
C
L
= 15 pF, R
L
= 2.0 kΩ
R
ext
= 5.0 kΩ
R
L
= 2.0 kΩ
C
ext
= 0
C
L
= 15 pF
Unit
Test Conditions
AC SETUP REQUIREMENTS
(T
A
= 25°C, V
CC
= 5.0 V)
Limits
Symbol
t
W
Pulse Width
Parameter
Min
40
Typ
Max
Unit
ns
Test Conditions
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