NA555, NE555, SA555, SE555
PRECISION TIMERS
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SLFS022F–SEPTEMBER 1973–REVISED JUNE 2006
APPLICATION INFORMATION (continued)
Sequential Timer
Many applications, such as computers, require signals for initializing conditions during start-up. Other
applications, such as test equipment, require activation of test signals in sequence. These timing circuits can be
connected to provide such sequential control. The timers can be used in various combinations of astable or
monostable circuit connections, with or without modulation, for extremely flexible waveform control. Figure 22
shows a sequencer circuit with possible applications in many systems, and Figure 23 shows the output
waveforms.
V
CC
4
8
4
8
V
CC
OUT
4
8
V
CC
33 kΩ
33 kΩ
RA
R
B
R
C
RESET
V
RESET
RESET
CC
OUT
3
7
6
3
7
6
3
7
2
5
2
5
2
OUT
TRIG
TRIG
TRIG
0.001
µF
0.001
µF
S
DISCH
DISCH
DISCH
THRES
5
CONT
CONT
CONT
6
THRES
THRES
GND
GND
GND
1
1
1
0.01
µF
0.01
µF
0.01
µF
C
C
C
B
C
A
C
C
R
C
= 14.7 µF
= 100 kΩ
C
= 10 µF
A
Output A
Output B
Output C
R
A
= 100 kΩ
C
B
= 4.7 µF
R
B
= 100 kΩ
Pin numbers shown are for the D, JG, P, PS, and PW packages.
NOTE A: S closes momentarily at t = 0.
Figure 22. Sequential Timer Circuit
See Figure 22
t A
w
t A = 1.1 R C
A A
w
Output A
Output B
Output C
t B
w
t B = 1.1 R C
w B B
t C = 1.1 R C
C C
w
t C
w
t = 0
t − Time − 1 s/div
Figure 23. Sequential Timer Waveforms
15
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