NE555, SA555, SE555, SE555C
PRECISION TIMERS
SLFS022 – D1669, SEPTEMBER 1973—REVISED FEBRUARY 1992
APPLICATION INFORMATION
Figure 13 shows typical waveforms generated during astable operation. The output high-level duration t
H
and
low-level duration t
L
may be calculated as follows:
f – Free-Running Frequency – Hz
+
0.693 (RA
)
RB) C
t L
+
0.693 (R B) C
tH
Other useful relationships are shown below.
period
100 k
RA + 2 RB = 1 kΩ
10 k
RA + 2 RB = 10 kΩ
RA + 2 RB = 100 kΩ
1k
+
tH
)
tL
+
0.693 (RA
)
2RB) C
1.44
frequency
[
(R
)
2R ) C
A
B
100
R
L
+
tH t
)
tL
+
R
)
B2R
B
A
tH
R
Output waveform duty cycle
+
+
1
*
R
)
B2R
tH
)
tL
Output driver duty cycle
A
Low
-
t o-high ratio
10
1
B
RA + 2 RB = 1 MΩ
RA + 2 RB = 10 MΩ
+
tL
tH
+
R
)
R
B
A
RB
0.1
0.001
0.01
0.1
1
10
100
C – Capacitance –
µF
Figure 14. Free-Running Frequency
missing-pulse detector
The circuit shown in Figure 15 may 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 continuously retriggered
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 illustrated in Figure 16.
VCC (5 V to 15 V)
2
TRIG
DISCH
7
5
0.01
µ
F
GND
1
C
A5T3644
Time – 0.1 ms/div
Pin numbers shown are shown for the D, JG, and P packages.
Figure 15. Circuit for Missing-Pulse Detector
Figure 16. Missing-Pulse Detector Waveform
POST OFFICE BOX 655303
•
DALLAS, TEXAS 75265
ÏÏÏÏÏ
CONT
THRES
6
ÏÏÏ
Output
3
Voltage – 2 V/div
Input
4
RESET
8
VCC
OUT
RL
RA
ÏÏÏÏÏ
ÏÏÏÏÏ
ÏÏÏÏÏ
ÏÏÏÏÏ
VCC = 5 V
RA = 1 kΩ
C = 0.1
µF
See Figure 15
Input Voltage
Output Voltage
Capacitor Voltage
11
TI [ TEXAS INSTRUMENTS ]
