The IC is
made up of a combination of linear comparators and digital flip-flops. The
entire circuit is usually housed in an 8-pin package.
 |
| 555 IC Pin-out |
Pin-out:
The
connection of the pins for a DIP package is as follows:
Pin
|
Name
|
Purpose
|
1
|
GND
|
Ground reference voltage, low
level (0 V)
|
2
|
TRIG
|
The OUT pin goes high and a timing
interval starts when this input falls below 1/2 of CTRL voltage (which is
typically 1/3 of VCC, when CTRL is open).
|
3
|
OUT
|
This output is driven to
approximately 1.7 V below +VCC or GND.
|
4
|
RESET
|
A timing interval may be reset by
driving this input to GND, but the timing does not begin again until RESET
rises above approximately 0.7 volts. Overrides TRIG which overrides THR.
|
5
|
CTRL
|
Provides "control"
access to the internal voltage divider (by default, 2/3 VCC).
|
6
|
THR
|
The timing (OUT high) interval
ends when the voltage at THR is greater than that at CTRL (2/3 VCC
if CTRL is open).
|
7
|
DIS
|
Open collector output which may
discharge a capacitor between intervals. In phase with output.
|
8
|
VCC
|
Positive supply voltage, which is
usually between 3 and 15 V depending on the variation.
|
