M54HC123/123A
M74HC123/123A
DUAL RETRIGGERABLE MONOSTABLE MULTIVIBRATOR
.
.
.
.
.
.
.
.
.
HIGH SPEED
t
PD
= 25 ns (TYP) at V
CC
= 5V
LOW POWER DISSIPATION
STANDBY STATE I
CC
=4
µA
(MAX.) AT T
A
=25°C
ACTIVE STATE I
CC
= 200
µA
(TYP.) AT V
CC
=5V
HIGH NOISE IMMUNITY
V
NIH
= V
NIL
= 28 % V
CC
(MIN.)
OUTPUT DRIVE CAPABILITY
10 LSTTL LOADS
SYMMETRICAL OUTPUT IMPEDANCE
I
OH
= I
OL
= 4 mA (MIN.)
BALANCED PROPAGATION DELAYS
t
PLH
= t
PHL
WIDE OPERATING VOLTAGE RANGE
V
CC
(OPR) = 2 V TO 6 V
WIDE OUTPUT PULSE WIDTH RANGE
t
WOUT
= 120 ns
∼
60 s OVER AT V
CC
= 4.5 V
PIN AND FUNCTION COMPATIBLE WITH
54/74LS123
B1R
(Plastic Package)
F1R
(Ceramic Package)
M1R
(Micro Package)
C1R
(Chip Carrier)
ORDER CODES :
M54HCXXXF1R
M74HCXXXM1R
M74HCXXXB1R
M74HCXXXC1R
DESCRIPTION
The M54/74HC123 is a high speed CMOS MONO-
STABLE multivibrator fabricated with silicon gate
C
2
MOS technology. It achieves the high speed
operation similar to equivalent LSTTL while main-
taining the CMOS low power dissipation. There are
two trigger inputs, A INPUT (negative edge) and 8
INPUT (positive edge). These inputs are valid for
slow rising/falling signals, (tr = tf = I sec). The device
may also be triggered by using the CLR input (posi-
tive-edge) because of the Schmitt-trigger input ;
after triggering the output maintains the MONO-
STABLE state for the time period determined by the
external resistor Rx and capacitor Cx. When Cx
≥
10nF and Rx
≥
10KΩ, the output pulse width value
is approssimatively given by the formula: t
w(out)
= K
•
Cx
•
Rx.
Two different pulse width constant are available:
K
≅
0.45 for HC123 K
≅
1 for HC123A.
Taking CLR low breaks this MONOSTABLE
STATE. If the next trigger pulse occurs during the
MONOSTABLEperiod it makes the MONOSTABLE
period longer. Limit for values of Cx and Rx :
Cx : NO LIMIT
Rx : V
CC
< 3.0 V 5 K
Ω
to 1 M
Ω
V
CC
≥
3.0 V 1 K
Ω
to 1 M
Ω
All inputs are equipped with protection circuits
PIN CONNECTIONS
(top view)
NC =
No Internal
Connection
October 1993
1/14
M54/M74HC123/123A
SYSTEM DIAGRAM
TIMING CHART
2/14
M54/M74HC123/123A
BLOCK DIAGRAM
Note :
(1) Cx, Rx, Dx are external components.
(2) Dx is a clamping diode.
The external capacitor is charged to V
CC
inthe stand-by state, i.e. no trigger. When the supply voltage is turned off Cx is discharged mainly
through an internal parasitic diode (see figures). If Cx is sufficiently large and V
CC
decreases rapidy, there will be some possibility of da-
maging the I.C. with a surge current or latch-up. If the voltage supply filter capacitor is large enough and V
CC
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. In cases where Cx is large the time taken for the supply voltage to fall to 0.4 V
CC
can be calculated as follows :
t
f
≥
(V
CC
– 0.7)
⋅
Cx/20mA
In cases where t
f
is too short an external clamping diode is required to protect the I.C. from the surge current.
FUNCTIONAL DESCRIPTION
STAND-BY STATE
The external capacitor, Cx, is fully charged to V
CC
in the stand-by state. Hence, before triggering, tran-
sistor Qp and Qn (connected to the Rx/Cx node) are
both turned-off. The two comparators that control
the timing and the two reference voltage sources
stop operating. The total supply current is therefore
only leakage current.
TRIGGER OPERATION
Triggering occurs when :
1 st) A is ”low” and B has a falling edge ;
2 nd) B is ”high” and A has a rising edge ;
3 rd) A is low and B is high and C1 has a rising edge.
After the multivibrator has been retriggered com-
parator C1 and C2 start operating and Qn is turned
on. Cx then discharges through Qn. The voltage at
the node R/C external falls.
When it reaches V
REFL
the output of comparator C1
becomes low. This in turn resets the flip-flop and Qn
is turned off.
At this point C1 stops functioning but C2 continues
to operate.
The voltage at R/C external begins to rise with a time
constant set by the external components Rx, Cx.
Triggering the multivibrator causes Q to go high after
internal delay due to the flip-flop and the gate. Q re-
mains high until the voltage at R/C external rises
again to V
REFH
. At this point C2 output goes low and
O goes low. C2 stop operating. That means that
after triggering when the voltage R/C external re-
turns to V
REFH
the multivibrator has returned to its
MONOSTABLE STATE. In the case where Rx
⋅
Cx
are large enough and the discharge time of the ca-
pacitor and the delay time in the I.C. can be ignored,
the width of the output pulse tw (out) is as follows :
t
W(OUT)
= 0.46 Cx
⋅
Rx (HC123)
t
W(OUT)
= Cx
⋅
Rx (HC123A)
3/14
M54/M74HC123/123A
FUNCTIONAL DESCRIPTION (continued)
RE-TRIGGERED OPERATION
When a second trigger pulse follows the first its ef-
fect will depend on the state of the multivibrator. If
the capacitor Cx is being charged the voltage level
of R/C external falls to Vrefl again and Q remains
high i.e. the retrigger pulse arrives in a time shorter
than the period Rx
⋅
Cx seconds, the capacitor
charging time constant. If the second trigger pulse
is very close to the initial trigger pulse it is ineffective
; i.e. the second trigger must arrive in the capacitor
discharge cycle to be ineffective; Hence the mini-
TRUTH TABLE
INPUTS
A
X
H
L
L
X
B
H
L
X
H
X
L
L
H
CL
H
H
H
H
Q
L
L
OUTPUTS
Q
H
H
OUTPUT ENABLE
INHIBIT
INHIBIT
OUTPUT ENABLE
OUTPUT ENABLE
INHIBIT
NOTE
mum time for a second trigger to be effective de-
pends on V
CC
and Cx.
RESET OPERATION
CL is normally high. If CL is low, the trigger is not ef-
fective because Q output goes low and trigger con-
trol flip-flop is reset.
Also transistor Op is turned on and Cx is charged
quicky to V
CC
. This means if CL input goes low, the
IC becomes waiting state both in operating and non
operating state.
X: Don’t Care Z: High Impedance
INPUT AND OUTPUT EQUIVALENT CIRCUIT
4/14
M54/M74HC123/123A
PIN DESCRIPTION
PIN No
1, 9
2, 10
3, 11
SYMBOL
1A, 2A
1B, 2B
1CLR,
2CLR
1Q, 2Q
2R
EXT
/C
EXT
1Q, 2Q
1C
EXT
2C
EXT
1R
EXT
/C
EXT
GND
V
CC
NAME AND FUNCTION
Trigger Inputs (Negative
Edge Triggered)
Trigger Inputs (Positive
Edge Triggered)
Direct Reset LOW and
Trigger Action at Positive
Edge
Outputs (Active LOW)
External Resistor
Capacitor Connection
Outputs (Active HIGH)
External Capacitor
Connection
External Resistor
Capacitor Connection
Ground (0V)
Positive Supply Voltage
IEC LOGIC SYMBOL
4, 12
7
13, 5
14, 6
15
8
16
ABSOLUTE MAXIMUM RATING
Symbol
V
CC
V
I
V
O
I
IK
I
OK
I
O
I
CC
or I
GND
P
D
T
stg
T
L
Supply Voltage
DC Input Voltage
DC Output Voltage
DC Input Diode Current
DC Output Diode Current
DC Output Source Sink Current Per Output Pin
DC V
CC
or Ground Current
Power Dissipation
Storage Temperature
Lead Temperature (10 sec)
Parameter
Value
-0.5 to +7
-0.5 to V
CC
+ 0.5
-0.5 to V
CC
+ 0.5
±
20
±
20
±
25
±
50
500 (*)
-65 to +150
300
Unit
V
V
V
mA
mA
mA
mA
mW
o
o
C
C
Absolute Maximum Ratings are those values beyond which damage to the device may occur. Functional operation under these condition isnotimplied.
(*) 500 mW:
≅
65
o
C derate to 300 mW by 10mW/
o
C: 65
o
C to 85
o
C
5/14
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