lm555jan National Semiconductor Corporation, lm555jan Datasheet - Page 8

• Manufacturer Part Number: lm555jan
• Description: Timer
• Manufacturer: National Semiconductor Corporation

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Applications Information
MONOSTABLE OPERATION
In this mode of operation, the timer functions as a one-shot
(Figure
by a transistor inside the timer. Upon application of a negative
trigger pulse of less than 1/3 V
which both releases the short circuit across the capacitor and
drives the output high.
The voltage across the capacitor then increases exponential-
ly for a period of t = 1.1 R
voltage equals 2/3 V
flop which in turn discharges the capacitor and drives the
output to its low state.
ated in this mode of operation. Since the charge and the
threshold level of the comparator are both directly proportion-
al to supply voltage, the timing interval is independent of
supply.
V
TIME = 0.1 ms/DIV.
R
C = 0.01μF
During the timing cycle when the output is high, the further
application of a trigger pulse will not effect the circuit so long
as the trigger input is returned high at least 10μs before the
end of the timing interval. However the circuit can be reset
CC
A
= 9.1kΩ
= 5V
1). The external capacitor is initially held discharged
FIGURE 2. Monostable Waveforms
FIGURE 1. Monostable
Bottom Trace: Capacitor Voltage 2V/Div.
Top Trace: Input 5V/Div.
Middle Trace: Output 5V/Div.
CC
Figure 2
. The comparator then resets the flip-
A
C, at the end of which time the
CC
shows the waveforms gener-
to pin 2, the flip-flop is set
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8
during this time by the application of a negative pulse to the
reset terminal (pin 4). The output will then remain in the low
state until a trigger pulse is again applied.
When the reset function is not in use, it is recommended that
it be connected to V
gering.
Figure 3
for various time delays.
NOTE: In monostable operation, the trigger should be driven
high before the end of timing cycle.
ASTABLE OPERATION
If the circuit is connected as shown in
connected) it will trigger itself and free run as a multivibrator.
The external capacitor charges through R
charges through R
by the ratio of these two resistors.
In this mode of operation, the capacitor charges and dis-
charges between 1/3 V
mode, the charge and discharge times, and therefore the fre-
quency are independent of the supply voltage.
is a nomograph for easy determination of R, C values
FIGURE 3. Time Delay
B
. Thus the duty cycle may be precisely set
FIGURE 4. Astable
CC
CC
to avoid any possibility of false trig-
and 2/3 V
CC
Figure 4
. As in the triggered
A
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+ R
(pins 2 and 6
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B
and dis-