SNAS548C – FEBRUARY 2000 – REVISED MARCH 2013
Figure 14. Time Delay
ASTABLE OPERATION
If the circuit is connected as shown in
(pins 2 and 6 connected) it will trigger itself and free run as a
multivibrator. The external capacitor charges through R
A
+ R
B
and discharges through R
B
. Thus the duty cycle
may be precisely set by the ratio of these two resistors.
Figure 15. Astable
In this mode of operation, the capacitor charges and discharges between 1/3 V
CC
and 2/3 V
CC
. As in the
triggered mode, the charge and discharge times, and therefore the frequency are independent of the supply
voltage.
shows the waveforms generated in this mode of operation.
V
CC
= 5V
TIME = 20μs/DIV.
R
A
= 3.9kΩ
R
B
= 3kΩ
C = 0.01μF
Top Trace: Output 5V/Div.
Bottom Trace: Capacitor Voltage 1V/Div.
Figure 16. Astable Waveforms
8
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