SLFS022H – SEPTEMBER 1973 – REVISED JUNE 2010
tw − Output Pulse Duration − s
Voltage − 2 V/div
Figure 10. Typical Monostable Waveforms
Astable Operation
As shown in
adding a second resistor, R
B
, to the circuit of
and connecting the trigger input to
the threshold input causes the timer to self-trigger and run as a multivibrator. The capacitor C charges through
R
A
and R
B
and then discharges through R
B
only. Therefore, the duty cycle is controlled by the values of R
A
and
R
B
.
This astable connection results in capacitor C charging and discharging between the threshold-voltage level
(≉0.67 × V
CC
) and the trigger-voltage level (≉0.33 × V
CC
). As in the monostable circuit, charge and discharge
times (and, therefore, the frequency and duty cycle) are independent of the supply voltage.
V
CC
(5 V to 15 V)
0.01
µ
F
Voltage − 1 V/div
Open
(see Note A) 5
4
7
R
B
6
2
C
R
A
8
V
CC
R
L
3
OUT
Output
CONT
RESET
DISCH
THRES
TRIG
GND
1
t
H
t
L
Pin numbers shown are for the D, JG, P, PS, and PW packages.
NOTE A: Decoupling CONT voltage to ground with a capacitor can
improve operation. This should be evaluated for individual
applications.
Figure 12. Circuit for Astable Operation
Figure 13. Typical Astable Waveforms
10
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R
A
= 9.1 kΩ
C
L
= 0.01
µF
R
L
= 1 kΩ
See Figure 9
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10
R
A
= 10 MΩ
1
R
A
= 1 MΩ
10
−1
Input Voltage
10
−2
10
−3
R
A
= 100 kΩ
10
−4
R
A
= 10 kΩ
R
A
= 1 kΩ
10
−5
0.001
0.01
0.1
1
10
100
Output Voltage
Capacitor Voltage
Time − 0.1 ms/div
C − Capacitance −
µF
Figure 11. Output Pulse Duration vs Capacitance
R
A
= 5 kW
R
B
= 3 kW
C = 0.15 µF
R
L
= 1 kW
See Figure 12
Output Voltage
Capacitor Voltage
Time − 0.5 ms/div
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