SE555-SP Datasheet, PDF (9/18 Pages) Texas Instruments – QML CLASS V PRECISION TIMER

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ÏÏÏÏÏÏÏÏÏÏ _{RA = 9.1 kΩ}
ÏÏÏÏÏ _{CL = 0.01 µF}
R_L = 1 kΩ
ÏÏÏÏÏÏÏÏÏÏ _{See Figure 9}
Input Voltage
10
1
10^−1
R_A = 10 MΩ
R_A = 1 MΩ
10^−2
SE555-SP
SGLS401 – FEBRUARY 2010
Output Voltage
ÏÏÏÏÏÏÏÏÏÏÏÏÏÏÏÏÏÏÏÏÏÏÏÏ _{Capacitor Voltage}
Time − 0.1 ms/div
Figure 11. Typical Monostable Waveforms
10^−3
10^−4
R_A = 100 kΩ
R_A = 10 kΩ
R_A = 1 kΩ
10^−5
0.001
0.01
0.1
1
10
100
C − Capacitance − µF
Figure 12. Output Pulse Duration vs Capacitance
Astable Operation
As shown in Figure 13, adding a second resistor, R_B, to the circuit of Figure 10 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
(Ⅹ0.67 × V_CC) and the trigger-voltage level (Ⅹ0.33 × V_CC). As in the monostable circuit, charge and discharge
ÎÎÎÎÎÎÎÎÎÎ _{times (and, therefore, the frequency and duty cycle) are independent of the supply voltage.}
ÎÎÎÎÎÎÎÎÎÎ VCC
ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ ^{(5 V to 15 V)}
R_A = 5 kW
R_B = 3 kW
C = 0.15 µF
R_L = 1 kW
See Figure 12
0.01 mF
Open
RA
(see Note A) ₅
8
4 ^CONT
VCC
RL
RESET
RB
7 _DISCH
6 _THRES
3
OUT
Output
tH
2 _TRIG
GND
t_L
Output Voltage
C
1
NOTE A: Decoupling CONT voltage to ground with a capacitor
can improve operation. This should be evaluated for
individual applications.
Figure 13. Circuit for Astable Operation
Capacitor Voltage
Time − 0.5 ms/div
Figure 14. Typical Astable Waveforms
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