LM555CMX_12 FAIRCHILD [Fairchild Semiconductor], LM555CMX_12 Datasheet - Page 4

• Manufacturer Part Number: LM555CMX_12
• Description: Single Timer
• Manufacturer: FAIRCHILD [Fairchild Semiconductor]

LM555
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 timer's internal 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
4
Vcc / 3 < V
Trigger
Threshold Voltage
Figure 3. Waveforms of Monostable Operation
R
V
V
(V
L
th
Don't care
th
th
> 2Vcc / 3
Figure 1. Monostable Circuit
< Vcc / 3
)(PIN 6)
th
3
2
< 2 Vcc / 3
OUT
TRIG
RESET
4
GND
1
Vcc / 3 < V
THRES
Vcc
DISCH
CONT
8
Trigger Voltage
V
V
(V
th
Don't care
th
tr
> 2Vcc / 3
< Vcc / 3
6
)(PIN 2)
7
5
th
Table 1. Basic Operating Table
< 2 Vcc / 3
C2
+Vcc
R
C1
A
Reset(PIN 4)
High
High
High
Low
Figure 2. Resistance and Capacitance vs.
10
10
10
10
10
10
-1
-2
-3
2
1
0
10
-5
10
-4
Time delay(t
Output(PIN 3)
10
-3
High
Low
Low
-
Time Delay(s)
10
-2
d
)
10
-1
10
0
Discharging Tr.
10
(PIN 7)
1
OFF
ON
ON
-
10
2