Datasheet

LM555 — Single Timer
© 2002 Fairchild Semiconductor Corporation www.fairchildsemi.com
LM555 Rev. 1.1.0 9
5. Pulse Position Modulation
If the modulating signal is applied to the control terminal while the timer is connected for the astable operation, as in
Figure 12, the timer becomes a pulse position modulator.
In the pulse position modulator, the reference of the timer's internal comparators is modulated, which modulates the
timer output according to the modulation signal applied to the control terminal.
Figure 13 illustrates a sine wave for modulation signal and the resulting output pulse position modulation; however, any
wave shape be used
.
6. Linear Ramp
When the pull-up resistor RA in the monostable circuit shown in Figure 2 is replaced with constant current source, the
V
C1
increases linearly, generating a linear ramp. Figure 14 shows the linear ramp generating circuit and Figure 15 illus-
trates the generated linear ramp waveforms.
Figure 12. Circuit for Pulse Position Modluation
Figure 13. Wafeforms of pulse position modulation
Figure 14. Circuit for Linear Ramp
Figure 15. Waveforms of Linear Ramp
84
7
1
2
3
5
6
CONT
GND
Vcc
DISCH
THRES
RESET
TRIG
OUT
+Vcc
R
A
C
R
B
Modulation
Output
1
5
6
7
8
4
2
3
RESET
Vcc
DISCH
THRES
CONT
GND
OUT
TRIG
+Vcc
C2
R1
R2
C1
Q1
Output
R
E