monostable multivibrator. 74HC4538 Datasheet

74HC4538 multivibrator. Datasheet pdf. Equivalent

74HC4538 Datasheet
Recommendation 74HC4538 Datasheet
Part 74HC4538
Description Dual retriggerable precision monostable multivibrator
Feature 74HC4538; M54HC4538 M74HC4538 DUAL RETRIGGERABLE MONOSTABLE MULTIVIBRATOR . . . . . . . . HIGH SPEED tPD = 2.
Manufacture ST Microelectronics
Datasheet
Download 74HC4538 Datasheet




ST Microelectronics 74HC4538
M54HC4538
M74HC4538
DUAL RETRIGGERABLE MONOSTABLE MULTIVIBRATOR
. HIGH SPEED
tPD = 25 ns (TYP.) AT VCC = 5 V
. LOW POWER DISSIPATION
STANDBY STATEICC =4 µA (MAX.) AT TA = 25 °C
ACTIVE STATE ICC = 200 µA (TYP.) AT VCC = 5 V
. HIGH NOISE IMMUNITY
VNIH = VNIL = 28 % VCC (MIN.)
. OUTPUT DRIVE CAPABILITY
10 LSTTL LOADS
. BALANCED PROPAGATION DELAYS
tPLH = tPHL
. WIDE OUTPUT PULSE WIDTH RANGE
tWOUT = 120 ns ~ 60 s OVER AT VCC = 4.5 V
. OUTPUT PULSE WIDTH INDEPENDENT
FROM TRIGGER INPUT PULSE WIDTH
. PIN AND FUNCTION COMPATIBLE
WITH 4538B
B1R
(Plastic Package)
F1R
(Ceramic Package)
M 1R
(Micro Package)
C1R
(Chip Carrier)
ORDER CODES :
M54HC4538F1R M74HC4538M1R
M74HC4538B1R M74HC4538C1R
PIN CONNECTIONS (top view)
DESCRIPTION
The M54/74HC4538 is a high speed CMOS DUAL
MONOSTABLEMULTIVIBRATOR fabricated in sili-
con gate C2MOS technology. It has the same high
speed performance of LSTTL combined with true
CMOS low power consumption. Each multivibrator
features both a negative, A, and a positive, B, edge
triggered input, either of which can be used as an in-
hibit input. Also included is a clear input that when
taken low resets the one shot. The monostable
multivibrators are retriggerable. That is, they may be
triggered reapeatedly while their outputs are gener-
ating 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 output pulse equation is simply :
PW = 0.7 (R)(C) where PW is in seconds, R in
Ohms, and C is in Farads.
All inputs are equipped with protection circuits
against static discharge and transient excess volt-
age.
October 1993
NC =
No Internal
Connection
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ST Microelectronics 74HC4538
M54/M74HC4538
SYSTEM DIAGRAM
TIMING CHART
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ST Microelectronics 74HC4538
BLOCK DIAGRAM
M 54/ M74H C4538
Notes : 1. Cx, Rx, Dx are external components.
2. Dx is a clamping diode.
3. The external capacitor is charged to VCC in the stand-by state, i.e. no trigger. When the supply voltage is turned off Cx is discharged
mainlythrough an internal parasitic diode (see figures). IfCx is sufficiently largeand VCC decreases rapidy, there willbesome possibility
of damaging the I.C. with a surge current or latch-up. If the voltage supply filter capacitor is large enough and VCC decrease slowly,
the surge current is automatically limited and damage the I.C. is avoided. The maximum forward current of the parasitic diode is ap-
proximately 20 mA. In cases where Cx is large the time taken for the supply voltage to fall to 0.4 VCC can be calculated as follows :
tf (VCC – 0.7) Cx/20 mA
In cases where tf is too short an external champing 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 VCC
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 ;
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 Rx/Cx external falls.
When it reaches VREFL 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 VREFH. At this point C2 output goes low and
G goes low. C2 stops operating. That means that
after triggering when the voltage at R/C external re-
turns to VREFH 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 :
tW(OUT) = 0.72 Cx Rx
RE-TRIGGER 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 Rx/Cx 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, trr (Min.) depends on VCC and Cx.
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