LM555/NE555/SA555
4
44
4
Application Information
Application InformationApplication Information
Application Information
Table 1 below is the basic operating table of 555 timer:
When the low signal input is applied to the reset terminal, the timer output remains low regardless of the threshold voltage or
the trigger voltage. Only when the high signal is applied to the reset terminal, the timer's output changes according to
threshold voltage and trigger voltage.
When the threshold voltage exceeds 2/3 of the supply voltage while the timer output is high, the time r's inter na l discharge Tr.
turns on, lowering the threshold voltage to below 1/3 of the supply voltage. During this time, the timer output is maintained
low. Later, if a low signal is applied to the trigger voltage so that it becomes 1/3 of the supply voltage, the timer's internal
discharge Tr. turns off, increasing the threshold voltage and driving the timer output again at high.
1. Monostable Operation
1. Monostable Operation1. Monostable Operation
1. Monostable Operation
Table 1. Basic Operating Table
Table 1. Basic Operating TableTable 1. Basic Operating Table
Table 1. Basic Operating Table
Threshold Voltage
Threshold Voltage Threshold Voltage
Threshold Voltage
(V
(V(V
(Vth
thth
th)(PIN 6)
)(PIN 6))(PIN 6)
)(PIN 6) Trigger Voltage
Trigger VoltageTrigger Voltage
Trigger Voltage
(V
(V(V
(Vtr
trtr
tr)(PIN 2)
)(PIN 2))(PIN 2)
)(PIN 2) Reset(PIN 4)
Reset(PIN 4)Reset(PIN 4)
Reset(PIN 4) Output(PIN 3)
Output(PIN 3)Output(PIN 3)
Output(PIN 3) Discharging Tr.
Discharging Tr.Discharging Tr.
Discharging Tr.
(PIN 7)
(PIN 7)(PIN 7)
(PIN 7)
Don't care Don't care Low Low ON
Vth > 2Vcc / 3 Vth > 2Vcc / 3 High Low ON
Vcc / 3 < Vth < 2 Vcc / 3 Vcc / 3 < Vth < 2 Vcc / 3 High - -
Vth < Vcc / 3 Vth < Vcc / 3 High High OFF
10
1010
10-5
-5-5
-5 10
1010
10-4
-4-4
-4 10
1010
10-3
-3-3
-3 10
1010
10-2
-2-2
-2 10
1010
10-1
-1-1
-1 10
1010
100
00
010
1010
101
11
110
1010
102
22
2
10
1010
10-3
-3-3
-3
10
1010
10-2
-2-2
-2
10
1010
10-1
-1-1
-1
10
1010
100
00
0
10
1010
101
11
1
10
1010
102
22
2
10M
10M10M
10MΩ
ΩΩ
Ω
1M
1M1M
1MΩ
ΩΩ
Ω
10k
10k10k
10kΩ
ΩΩ
Ω
100k
100k100k
100kΩ
ΩΩ
Ω
R
RR
RA
AA
A=1k
=1k=1k
=1kΩ
ΩΩ
Ω
Capacitance(uF)
Capacitance(uF)Capacitance(uF)
Capacitance(uF)
Ti m e D el a y(s)
Ti m e D el a y(s)Ti m e D el a y(s)
Ti m e D el a y(s)
Figure 1. Monoatable Circuit
Figure 1. Monoatable CircuitFigure 1. Monoatable Circuit
Figure 1. Monoatable Circuit Figure 2. Resistance and Capacitance vs.
Figure 2. Resistance and Capacitance vs.Figure 2. Resistance and Capacitance vs.
Figure 2. Resistance and Capacitance vs.
Time delay(t
Time delay(tTime delay(t
Time delay(td
dd
d)
))
)
Figure 3. Waveforms of Monostable Operation
Figure 3. Waveforms of Monostable OperationFigure 3. Waveforms of Monostable Operation
Figure 3. Waveforms of Monostable Operation
1
5
6
7
8
4
2
3
RESET Vcc
DISCH
THRES
CONT
GND
OUT
TRIG
+Vcc
RA
C1
C2RL
Trigger