SE555-SP Datasheet, PDF (10/18 Pages) Texas Instruments – QML CLASS V PRECISION TIMER

SE555-SP
SGLS401 – FEBRUARY 2010
www.ti.com
Figure 13 shows typical waveforms generated during astable operation. The output high-level duration t_H and
low-level duration t_L can be calculated as follows:
t
H
=
0.693
(R_A
+
R_B)
C
(1)
t
L
=
0.693
(R_B)
C
(2)
Other useful relationships are shown in the following equations.
period = t_H + t_L = 0.693 (R_A + 2R_B) C
(3)
frequency
»
1.44
(^¾ R_A + 2R_B) C
(4)
Output
driver
duty
cycle
=
t_L
t^¾ _H + t_L
=
R_B
R^¾ _A + 2R_B
(5)
Output
waveform
duty
cycle
=
t_H
t^¾ _H + t_L
=1
-
R_B
R^¾ _A + 2R_B
(6)
Low-to-high
ratio
=
t_L
¾_tH
=
R_B
R^¾ _A + R_B
(7)
100 k
10 k
R_A + 2 R_B = 1 kΩ
R_A + 2 R_B = 10 kΩ
R_A + 2 R_B = 100 kΩ
1k
100
10
1
R_A + 2 R_B = 1 MΩ
R_A + 2 R_B = 10 MΩ
0.1
0.001
0.01
0.1
1
10
100
C − Capacitance − µF
Figure 15. Free-Running Frequency
10
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