Datasheet

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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
+
t
L
t
H
+
R
B
R
A
) R
B
Low-to-high ratio
+
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
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
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
4 8
3
7
6
2
5
1
Pin numbers shown are shown for the D, JG, P, PS, and PW packages.
NA555 , NE555 , SA555 , SE555
PRECISION TIMERS
SLFS022F – SEPTEMBER 1973 – REVISED JUNE 2006
APPLICATION INFORMATION (continued)
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:
Figure 14. Free-Running Frequency
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 Figure 16. Completed Timing Waveforms for
Missing-Pulse Detector
11
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