LM555CMX_12 FAIRCHILD [Fairchild Semiconductor], LM555CMX_12 Datasheet - Page 6

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

LM555
An astable timer operation is achieved by adding resistor R
operation, the trigger terminal and the threshold terminal are connected so that a self-trigger is formed, operating as a multi
vibrator. When the timer output is high, its internal discharging Tr. turns off and the V
function with the time constant (R
When the V
resetting the F/F and causing the timer output to become low. This in turn turns on the discharging Tr. and the C1 discharges
through the discharging channel formed by R
output on the trigger terminal becomes high and the timer output becomes high again. The discharging Tr. turns off and the
V
In the above process, the section where the timer output is high is the time it takes for the V
and the section where the timer output is low is the time it takes for the V
is high, the equivalent circuit for charging capacitor C1 is as follows:
Since the duration of the timer output high state(t
6
C1
Vcc
rises again.
V
C1
t  
C1
C 1
=
, or the threshold voltage, reaches 2Vcc/3, the comparator output on the trigger terminal becomes high,
V
C1
dv c1
------------ -
V
CC
dt
R

0+
A




=
1

–
V cc V 0-
------------------------------ -
=
R
2
-- - e
3
V
A
-
–
CC


+
–
------------------------------------

R
R
R A

3 
B
B
A
Figure 7. Waveforms of Astable Operation
+
+R

R B
t
B
C1
C1
)*C.
2  
1  






B
and the discharging Tr. When the V
Vc1(0-)=Vcc/3
H
3  
) is the amount of time it takes for the V
B
to Figure 1 and configuring as shown on Figure 5. In the astable
C1
to drop from 2Vcc/3 to Vcc/3. When timer output
C1
C1
falls below Vcc/3, the comparator
increases by exponential
C1
C1
(t) to reach 2Vcc/3,
to rise from Vcc/3 to 2Vcc/3,