M54HC423/423A
M74HC423/423A
October 1993
DUAL RETRIGGERABLE MONOSTABLE MULTIVIBRATOR
B1R
(Plastic Package)
ORDER CODES :
M54HCXXXF1R
M74HCXXXM1R
M74HCXXXB1R
M74HCXXXC1R
F1R
(Ceramic Package)
M1R
(Micro Package)
C1R
(Chip Carrier)
PIN CONNECTIONS (top view)
NC =
No Internal
Connection
.
HIGH SPEED
t
PD
= 25 ns (TYP) at V
CC
= 5V
.
LOW POWER DISSIPATION
STANDBY STATE I
CC
=4
A (MAX.) AT T
A
=25
C
ACTIVE STATE I
CC
= 700
A (MAX.) 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
54/74LS423
The M54/74HC423/423A are high speed CMOS
MONOSTABLE
multivibrators
fabricated
with
silicon gate C
2
MOS technology.
They achieve the high speed operation similar to
equivalent LSTTL while maintaining the CMOS low
power dissipation. There are two trigger inputs, A
INPUT (negative edge) and B INPUT (positive
edge). These inputs are valid for rising/falling
signals, (t
r
t
f
1 sec). After triggering the output
maintains the MONOSTABLE state for the time
period determined by the external resistor Rx and
capacitor Cx.
Two different pulse width constant are available:
K
0.46 for HC423
K
1 for HC423A.
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
to 1 M
V
CC
3.0 V 1 K
to 1 M
All inputs are equipped with protection circuits
against static discharge and transient excess
voltage.
DESCRIPTION
1/14
SYSTEM DIAGRAM
TIMING CHART
M54/M74HC423/423A
2/14
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,
transistor 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
comparator 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
remains 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
returns 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
capacitor 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 (HC423)
t
W(OUT)
= Cx
Rx (HC423A)
M54/M74HC423/423A
3/14
FUNCTIONAL DESCRIPTION (continued)
RE-TRIGGERED OPERATION
When a second trigger pulse follows the first its
effect 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
minimum time for a second trigger to be effective
depends on V
CC
and Cx.
RESET OPERATION
CL is normally high. If CL is low, the trigger is not
effective because Q output goes low and trigger
control 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.
TRUTH TABLE
INPUTS
OUTPUTS
NOTE
A
B
CL
Q
Q
H
H
OUTPUT ENABLE
X
L
H
L
H
INHIBIT
H
X
H
L
H
INHIBIT
L
H
OUTPUT ENABLE
X
X
L
L
H
INHIBIT
X: Don't Care Z: High Impedance
INPUT AND OUTPUT EQUIVALENT CIRCUIT
M54/M74HC423/423A
4/14
PIN DESCRIPTION
PIN No
SYMBOL
NAME AND FUNCTION
1, 9
1A, 2A
Trigger Inputs (Negative
Edge Triggered)
2, 10
1B, 2B
Trigger Inputs (Positive
Edge Triggered)
3, 11
1CLR,
2CLR
Direct Reset (Active LOW)
4, 12
1Q, 2Q
Outputs (Active LOW)
7
2R
EXT
/C
EXT
External Resistor
Capacitor Connection
13, 5
1Q, 2Q
Outputs (Active HIGH)
14, 6
1C
EXT
2C
EXT
External Capacitor
Connection
15
1R
EXT
/C
EXT
External Resistor
Capacitor Connection
8
GND
Ground (0V)
16
V
CC
Positive Supply Voltage
IEC LOGIC SYMBOL
ABSOLUTE MAXIMUM RATING
Symbol
Parameter
Value
Unit
V
CC
Supply Voltage
-0.5 to +7
V
V
I
DC Input Voltage
-0.5 to V
CC
+ 0.5
V
V
O
DC Output Voltage
-0.5 to V
CC
+ 0.5
V
I
IK
DC Input Diode Current
20
mA
I
OK
DC Output Diode Current
20
mA
I
O
DC Output Source Sink Current Per Output Pin
25
mA
I
CC
or I
GND
DC V
CC
or Ground Current
50
mA
P
D
Power Dissipation
500 (*)
mW
T
stg
Storage Temperature
-65 to +150
o
C
T
L
Lead Temperature (10 sec)
300
o
C
Absolute Maximum Ratings are those values beyond which damage to the device may occur. Functional operation under these condition is not implied.
(*) 500 mW:
65
o
C derate to 300 mW by 10mW/
o
C: 65
o
C to 85
o
C
M54/M74HC423/423A
5/14
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