tm
74VHC123A Dual Retriggerable Monostable Multivibrator
May 2007
©1993 Fairchild Semiconductor Corporation www.fairchildsemi.com
74VHC123A Rev. 1.2
74VHC123A
Dual Retriggerable Monostable Multivibrator
Features
■
High Speed: t
PD
=
8.1ns (Typ.) at T
A
=
25°C
■
Low Power Dissipation: I
CC
=
4µA (Max) at T
A
=
25°C
■
Active State: I
CC
=
600µA (Max.) at T
A
=
25°C
■
High Noise Immunity: V
NIH
=
V
NIL
=
28% V
CC
(Min.)
■
Power down protection is provided on all inputs
■
Pin and function compatible with 74HC123A
General Description
The VHC123A is an advanced high speed CMOS
Monostable Multivibrator fabricated with silicon gate
CMOS technology. It achieves the high speed operation
similar to equivalent Bipolar Schottky TTL while main-
taining the CMOS low power dissipation. Each multi-
vibrator features both a negative, A, and a positive, 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 VHC123A can be
triggered on the positive transition of the clear while A is
held low and B is held high. The output pulse width is
determined by the equation: PW
=
(R
x
)(C
x
); where PW
is in seconds, R is in ohms, and C is in farads.
Limits for R
x
and C
x
are:
External capacitor, C
x
: No limit
External resistors, R
x
:V
CC
=
2.0V, 5 k
Ω
min
V
CC
>
3.0V, 1 k
Ω
min
An input protection circuit ensures that 0 to 7V can be
applied to the input pins without regard to the supply
voltage. This device can be used to interface 5V to 3V
systems and two supply systems such as battery back
up. This circuit prevents device destruction due to mis-
matched supply and input voltages.
Ordering Information
Surface mount packages are also available on Tape and Reel. Specify by appending the suffix letter “X” to the
ordering number.
Order Number
Package
Number Package Description
74VHC123AM M16A 16-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-012, 0.150” Narrow
74VHC123ASJ M16D 16-Lead Small Outline Package (SOP), EIAJ TYPE II, 5.3mm Wide
74VHC123AMTC MTC16 16-Lead Thin Shrink Small Outline Package (TSSOP), JEDEC MO-153, 4.4mm
Wide
74VHC123A Dual Retriggerable Monostable Multivibrator
©1993 Fairchild Semiconductor Corporation www.fairchildsemi.com
74VHC123A Rev. 1.2 2
Connection Diagram
Pin Description
Logic Symbol
IEEE/IEC
Truth Table
H
=
HIGH Voltage Level
L
=
LOW Voltage Level
=
HIGH-to-LOW Transition
=
LOW-to-HIGH Transition
X
=
Don't Care
Pin Names Description
ATrigger Inputs (Negative Edge)
BTrigger Inputs (Positive Edge)
CLR Reset Inputs
C
x
External Capacitor
R
x
External Resistor
Q, Q Outputs
Inputs Outputs
FunctionA B CLR QQ
HH Output Enable
XLHLHInhibit
HX HLHInhibit
LH Output Enable
LH Output Enable
XX LLHReset
74VHC123A Dual Retriggerable Monostable Multivibrator
©1993 Fairchild Semiconductor Corporation www.fairchildsemi.com
74VHC123A Rev. 1.2 3
Block Diagrams
Note A:
C
x
, R
x
, D
x
are external Capacitor, Resistor, and Diode, respectively.
Note B:
External clamping diode, D
x
;
External capacitor is charged to V
CC
level in the wait state, i.e. when no trigger is applied.
If the supply voltage is turned off, C
x
discharges mainly through the internal (parasitic) diode. If C
x
is sufficiently large
and V
CC
drops rapidly, there will be some possibility of damaging the IC through in rush current or latch-up. If the
capacitance of the supply voltage filter is large enough and V
CC
drops slowly, the in rush current is automatically
limited and damage to the IC is avoided.
The maximum value of forward current through the parasitic diode is ±20mA. In the case of a large Cx, the limit of fall
time of the supply voltage is determined as follows:
t
f
≥
(V
CC
–0.7) C
x
/ 20mA
(t
f
is the time between the supply voltage turn off and the supply voltage reaching 0.4 V
CC
)
In the event a system does not satisfy the above condition, an external clamping diode (D
x
) is needed to protect the IC
from rush current.
74VHC123A Dual Retriggerable Monostable Multivibrator
©1993 Fairchild Semiconductor Corporation www.fairchildsemi.com
74VHC123A Rev. 1.2 4
System Diagram
Timing Chart
74VHC123A Dual Retriggerable Monostable Multivibrator
©1993 Fairchild Semiconductor Corporation www.fairchildsemi.com
74VHC123A Rev. 1.2 5
Functional Description
1. Stand-by State
The external capacitor (C
x
) is fully charged to V
CC
in
the Stand-by State. That means, before triggering,
the Q
P
and Q
N
transistors which are connected to the
R
x
/C
x
node are in the off state. Two comparators that
relate to the timing of the output pulse, and two refer-
ence voltage supplies turn off. The total supply cur-
rent is only leakage current.
2. Trigger Operation
Trigger operation is effective in any of the following
three cases. First, the condition where the A input is
LOW, and B input has a rising signal; second, where
the B input is HIGH, and the A input has a falling sig-
nal; and third, where the A input is LOW and the B
input is HIGH, and the CLR input has a rising signal.
After a trigger becomes effective, comparators C
1
and C
2
start operating, and Q
N
is turned on. The
external capacitor discharges through Q
N
. The volt-
age level at the R
x
/C
x
node drops. If the R
x
/C
x
volt-
age level falls to the internal reference voltage V
ref
L,
the output of C
1
becomes LOW. The flip-flop is then
reset and Q
N
turns off. At that moment C
1
stops but
C
2
continues operating.
After Q
N
turns off, the voltage at the R
x
/C
x
node
starts rising at a rate determined by the time constant
of external capacitor C
x
and resistor R
x
.
Upon triggering, output Q becomes HIGH, following
some delay time of the internal F/F and gates. It stays
HIGH even if the voltage of R
x
/C
x
changes from fall-
ing to rising. When R
x
/C
x
reaches the internal refer-
ence voltage V
ref
H, the output of C
2
becomes LOW,
the output Q goes LOW and C
2
stops its operation.
That means, after triggering, when the voltage level
of the R
x
/C
x
node reaches V
ref
H, the IC returns to its
MONOSTABLE state.
With large values of C
x
and R
x
, and ignoring the dis-
charge time of the capacitor and internal delays of
the IC, the width of the output pulse, t
W
(OUT), is as
follows:
t
W
(OUT)
=
1.0 C
x
R
x
3. Retrigger operation (74VHC123A)
When a new trigger is applied to either input A or B
while in the MONOSTABLE state, it is effective only if
the IC is charging C
x
. The voltage level of the R
x
/C
x
node then falls to V
ref
L level again. Therefore the Q
output stays HIGH if the next trigger comes in before
the time period set by C
x
and R
x
.
If the new trigger is very close to a previous trigger,
such as an occurrence during the discharge cycle, it
will have no effect.
The minimum time for a trigger to be effective 2nd
trigger, t
RR
(Min), depends on V
CC
and C
x
.
4. Reset Operation
In normal operation, the CLR input is held HIGH. If
CLR is LOW, a trigger has no affect because the Q
output is held LOW and the trigger control F/F is
reset. Also, Q
p
turns on and C
x
is charged rapidly to
V
CC
.
This means if CLR is set LOW, the IC goes into a wait
state.
74VHC123A Dual Retriggerable Monostable Multivibrator
©1993 Fairchild Semiconductor Corporation www.fairchildsemi.com
74VHC123A Rev. 1.2 6
Absolute Maximum Ratings
Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be
operable above the recommended operating conditions and stressing the parts to these levels is not recommended.
In addition, extended exposure to stresses above the recommended operating conditions may affect device reliability.
The absolute maximum ratings are stress ratings only.
Recommended Operating Conditions(1)
The Recommended Operating Conditions table defines the conditions for actual device operation. Recommended
operating conditions are specified to ensure optimal performance to the datasheet specifications. Fairchild does not
recommend exceeding them or designing to absolute maximum ratings.
Notes:
1. Unused inputs must be held HIGH or LOW. They may not float.
2. The maximum allowable values of Cx and Rx are a function of the leakage of capacitor Cx, the leakage of the device,
and leakage due to board layout and surface resistance. Susceptibility to externally induced noise signals may occur
for Rx > 1MΩ.
Symbol Parameter Rating
VCC Supply Voltage –0.5V to +7.0V
VIN DC Input Voltage –0.5V to +7.0V
VOUT DC Output Voltage –0.5V to VCC + 0.5V
IIK Input Diode Current –20mA
IOK Output Diode Current ±20mA
IOUT DC Output Current ±25mA
ICC DC VCC / GND Current ±50mA
TSTG Storage Temperature –65°C to +150°C
TL Lead Temperature (Soldering, 10 seconds) 260°C
Symbol Parameter Rating
VCC Supply Voltage 2.0V to +5.5V
VIN Input Voltage 0V to +5.5V
VOUT Output Voltage 0V to VCC
TOPR Operating Temperature –40°C to +85°C
tr, tf Input Rise and Fall Time (CLR only)
V
CC = 3.3V ± 0.3V
V
CC = 5.0V ± 0.5V
0ns/V ∼ 100ns/V
0ns/V ∼ 20ns/V
External Capacitor, CxNo Limitation(2) F
External Resistor, Rx>5kΩ(2) (VCC = 2.0V)
>1kΩ(2) (VCC > 3.0V)
74VHC123A Dual Retriggerable Monostable Multivibrator
©1993 Fairchild Semiconductor Corporation www.fairchildsemi.com
74VHC123A Rev. 1.2 7
DC Electrical Characteristics
Note:
3. Per circuit.
Symbol Parameter VCC (V) Conditions
TA = 25°C TA = –40° to 85°C
UnitsMin. Typ. Max. Min. Max.
VIH HIGH Level Input
Voltage
2.0 1.50 1.50 V
3.0–5.5 0.7 x VCC 0.7 x VCC
VIL LOW Level Input
Voltage
2.0 0.50 0.50 V
3.0–5.5 0.3 x VCC 0.3 x VCC
VOH HIGH Level Output
Voltage
2.0 VIN = VIH
or VIL
IOH = –50µA 1.9 2.0 1.9 V
3.0 2.9 3.0 2.9
4.5 4.4 4.5 4.4
3.0 IOH = –4mA 2.58 2.48
4.5 IOH = –8mA 3.94 3.80
VOL LOW Level Output
Voltage
2.0 VIN = VIH
or VIL
IOL = 50µA 0.0 0.1 0.1 V
3.0 0.0 0.1 0.1
4.5 0.0 0.1 0.1
3.0 IOL = 4mA 0.36 0.44
4.5 IOL = 8mA 0.36 0.44
IIN Input Leakage
Current
0–5.5 VIN = 5.5V or GND ±0.1 ±1.0 µA
IIN Rx/Cx Terminal
Off-State Current
5.5 VIN = VCC or GND ±0.25 ±2.50 µA
ICC Quiescent Supply
Current
5.5 VIN = VCC or GND 4.0 40.0 µA
ICC Active—State(3)
Supply Current
3.0 VIN = VCC or GND,
Rx/Cx = 0.5 VCC
160 250 280 µA
4.5 380 500 650
5.5 560 750 975
74VHC123A Dual Retriggerable Monostable Multivibrator
©1993 Fairchild Semiconductor Corporation www.fairchildsemi.com
74VHC123A Rev. 1.2 8
AC Electrical Characteristics(4)
Notes:
4. Refer to Timing Chart.
5. CPD is defined as the value of the internal equivalent capacitance which is calculated from the operating current
consumption without load. Average operating current can be obtained by the equation:
ICC (opr.) = CPD • VCC • fIN+ ICC1 • Duty / 100 + ICC / 2 (per Circuit)
ICC1: Active Supply Current
Duty: %
Symbol Parameter VCC (V) Conditions
TA = 25°C
TA = –40°C
to +85°C
UnitsMin. Typ. Max. Min. Max.
tPLH, tPHL Propagation Delay Time
(A, B–Q, Q)
3.3 ± 0.3 CL = 15 pF 13.4 20.6 1.0 24.0 ns
CL = 50 pF 15.9 24.1 1.0 27.5
5.0 ± 0.5 CL = 15 pF 8.1 12.0 1.0 14.0 ns
CL = 50 pF 9.6 14.0 1.0 16.0
tPLH, tPHL Propagation Delay Time
(CLR Tr igger—Q, Q)
3.3 ± 0.3 CL = 15 pF 14.5 22.4 1.0 26.0 ns
CL = 50 pF 17.0 25.9 1.0 29.5
5.0 ± 0.5 CL = 15 pF 8.7 12.9 1.0 15.0 ns
CL = 50 pF 10.2 14.9 1.0 17.0
tPLH, tPHL Propagation Delay Time
(CLR—Q, Q)
3.3 ± 0.3 CL = 15 pF 10.3 15.8 1.0 18.5 ns
CL = 50 pF 12.8 19.3 1.0 22.0
5.0 ± 0.5 CL = 15 pF 6.3 9.4 1.0 11.0 ns
CL = 50 pF 7.8 11.4 1.0 13.0
tWOUT Output Pulse Width 3.3 ± 0.3 CL = 50pF, Cx = 28pF,
Rx = 2kΩ
160 240 300 ns
5.0 ± 0.5 133 200 240
3.3 ± 0.3 CL = 50pF, Cx = 0.01µF,
Rx = 10kΩ
90 100 110 90 110 µs
5.0 ± 0.5 90 100 110 90 110
3.3 ± 0.3 CL = 50pF, Cx = 0.1µF,
Rx = 1kΩ
0.9 1.0 1.1 0.9 1.1 ms
5.0 ± 0.5 0.9 1.0 1.1 0.9 1.1
∆tWOUT Output Pulse Width Error
Between Circuits
(In same Package)
±1 %
CIN Input Capacitance VCC = Open 4 10 10 pF
CPD Power Dissipation
Capacitance
(5) 73 pF
74VHC123A Dual Retriggerable Monostable Multivibrator
©1993 Fairchild Semiconductor Corporation www.fairchildsemi.com
74VHC123A Rev. 1.2 9
AC Operating Requirement(6)
Note:
6. Refer to Timing Chart.
Symbol Parameter VCC (V) Conditions
TA = 25°C
TA = –40°C
to +85°C
UnitsMin. Typ. Max. Min. Max.
tW(L), tW(H) Minimum Trigger
Pulse Width
3.3 5.0 5.0 ns
5.0 5.0 5.0
tW(L) Minimum Clear
Pulse Width
3.3 5.0 5.0 ns
5.0 5.0 5.0
tRR Minimum Retrigger
Time
3.3 ± 0.3 Rx = 1kΩ,
CX = 100pF
60 ns
5.0 ± 0.5 39
3.3 Rx = 1kΩ,
CX = 0.01µF
1.5 µs
5.0 1.2
74VHC123A Dual Retriggerable Monostable Multivibrator
©1993 Fairchild Semiconductor Corporation www.fairchildsemi.com
74VHC123A Rev. 1.2 10
Device Characteristics
twout*Cx Characteristics (Typ.)
Output Pulse Width Constant K-Supply Voltage
(Typ.)
tRR*VCC Characteristics (Typ.)
Input Equivalent Circuit
74VHC123A Dual Retriggerable Monostable Multivibrator
©1993 Fairchild Semiconductor Corporation www.fairchildsemi.com
74VHC123A Rev. 1.2 11
Physical Dimensions
Dimensions are in millimeters unless otherwise noted.
Figure 1. 16-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-012, 0.150" Narrow
Package Number M16A
74VHC123A Dual Retriggerable Monostable Multivibrator
©1993 Fairchild Semiconductor Corporation www.fairchildsemi.com
74VHC123A Rev. 1.2 12
Physical Dimensions (Continued)
Dimensions are in millimeters unless otherwise noted.
Figure 2. 16-Lead Small Outline Package (SOP), EIAJ TYPE II, 5.3mm Wide
Package Number M16D
74VHC123A Dual Retriggerable Monostable Multivibrator
©1993 Fairchild Semiconductor Corporation www.fairchildsemi.com
74VHC123A Rev. 1.2 13
Physical Dimensions (Continued)
Dimensions are in millimeters unless otherwise noted.
Figure 3. 16-Lead Thin Shrink Small Outline Package (TSSOP), JEDEC MO-153, 4.4mm Wide
Package Number MTC16
0.65
4.4±0.1
MTC16rev4
0.11
4.55
5.00
5.00±0.10
12°
7.354.45
1.45
5.90
74VHC123A Dual Retriggerable Monostable Multivibrator
©1993 Fairchild Semiconductor Corporation www.fairchildsemi.com
74VHC123A Rev. 1.2 14
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FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO ANY PRODUCTS
HEREIN TO IMPROVE RELIABILITY, FUNCTION OR DESIGN. FAIRCHILD DOES NOT ASSUME ANY LIABILITY ARISING OUT OF THE
APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN; NEITHER DOES IT CONVEY ANY LICENSE UNDER
ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS. THESE SPECIFICATIONS DO NOT EXPAND THE TERMS OF FAIRCHILD’S
WORLDWIDE TERMS AND CONDITIONS, SPECIFICALLY THE WARRANTY THEREIN, WHICH COVERS THESE PRODUCTS.
LIFE SUPPORT POLICY
FAIRCHILD’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR
SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF FAIRCHILD SEMICONDUCTOR CORPORATION.
As used herein:
1. Life support devices or systems are devices or systems
which, (a) are intended for surgical implant into the body or
(b) support or sustain life, and (c) whose failure to perform
when properly used in accordance with instructions for use
provided in the labeling, can be reasonably expected to
result in a significant injury of the user.
2. A critical component in any component of a life support,
device, or system whose failure to perform can be
reasonably expected to cause the failure of the life support
device or system, or to affect its safety or effectiveness.
PRODUCT STATUS DEFINITIONS
Definition of Terms
Datasheet Identification Product Status Definition
Advance Information Formative or In Design This datasheet contains the design specifications for product
development. Specifications may change in any manner without notice.
Preliminary This datasheet contains preliminary data; supplementary data will be
published at a later date. Fairchild Semiconductor reserves the right to
make changes at any time without notice to improve design.
No Identification Needed Full Production
First Production
This datasheet contains final specifications. Fairchild Semiconductor
reserves the right to make changes at any time without notice to improve
design.
Obsolete Not In Production This datasheet contains specifications on a product that has been
discontinued by Fairchild Semiconductor. The datasheet is printed for
reference information only.
Rev. I26
