Datasheet

NE555, NE555Y, SA555, SE555, SE555C
PRECISION TIMERS
SLFS022A – SEPTEMBER 1973 – REVISED SEPTEMBER 2000
11
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
Figure 13 shows typical waveforms generated during astable operation. The output high-level duration t
H
and
low-level duration t
L
can be calculated as follows:
t
H
0.693 (R
A
R
B)
C
t
L
0.693 (R
B)
C
Other useful relationships are shown below.
period t
H
t
L
0.693 (R
A
2R
B
)C
frequency
1.44
(R
A
2R
B
)C
Output driver duty cycle
t
L
t
H
t
L
R
B
R
A
2R
B
Output waveform duty cycle
Low t high ratio
t
L
t
H
R
B
R
A
R
B
-o-
t
H
t
H
t
L
1–
R
B
R
A
2R
B
f – Free-Running Frequency – Hz
C – Capacitance – µF
100 k
10 k
1 k
100
10
1
1001010.10.01
0.1
0.001
R
A
+ 2 R
B
= 10 MΩ
R
A
+ 2 R
B
= 1 MΩ
R
A
+ 2 R
B
= 100 kΩ
R
A
+ 2 R
B
= 10 kΩ
R
A
+ 2 R
B
= 1 kΩ
Figure 14. Free-Running Frequency
missing-pulse detector
The circuit shown in Figure 15 can be used to detect a missing pulse or abnormally long spacing between
consecutive pulses in a train of pulses. The timing interval of the monostable circuit is retriggered continuously
by the input pulse train as long as the pulse spacing is less than the timing interval. A longer pulse spacing,
missing pulse, or terminated pulse train permits the timing interval to be completed, thereby generating an
output pulse as shown in Figure 16.
Figure 15. Circuit for Missing-Pulse Detector
V
CC
(5 V to 15 V)
DISCH
OUT
V
CC
RESET
R
L
R
A
A5T3644
C
THRES
GND
CONT
TRIG
Input
0.01 µF
Output
48
3
7
6
2
5
1
Pin numbers shown are shown for the D, JG, and P packages.
Figure 16. Circuit for Missing-Pulse Detector
Time – 0.1 ms/div
Voltage – 2 V/div
V
CC
= 5 V
R
A
= 1 kΩ
C = 0.1 µF
See Figure 15
Capacitor Voltage
Output Voltage
Input Voltage