The NE555 devices are precision timing
circuits capable of producing accurate time delays
or oscillation. In time-delay or monostable operating
modes, the timed interval is controlled by a single
external resistor and capacitor network. In the astable
mode of operation, the frequency and duty cycle are
controlled independently with two external resistors
and a single external capacitor.
Each timer has a trigger level equal to approximately
one-third of the supply voltage and a threshold
level equal to approximately two-thirds of the supply
voltage. These levels can be altered by use of the
control voltage pin (CONT). When the trigger input
(TRIG) is less than the trigger level, the flip-flop is
set and the output goes high. If TRIG is greater than
the trigger level and the threshold input (THRES)
is greater than the threshold level, the flip-flop is
reset and the output is low. The reset input (RESET)
overrides all other inputs and is used to initiate a new
timing cycle. If RESET is low, the flip-flop is reset and
the output is low. Whenever the output is low, a lowimpedance path is provided between the discharge
pin (DISCH) and the ground pin (GND). Tie all unused
inputs to an appropriate logic level to prevent false
triggering.
The output circuit is capable of sinking or sourcing
current up to 200mA. Operation is specified for
supplies of 5V to 15V. With a 5V supply, output levels
are compatible with TTL inputs.
Features
- Timing from microseconds to hours
- Astable or monostable operation
- Adjustable duty cycle
- TTL-compatible output can sink or source
up to 200mA
- On products compliant to MIL-PRF-38535,
all parameters are tested unless otherwise noted.
Applications
- Pulse-shaping circuits
- Missing-pulse detectors
- Pulse-width modulators
- Pulse-position modulators
- Sequential timers
- Pulse generators
-F requency dividers
- Industrial controls