SLFS022 – D1669, SEPTEMBER 1973—REVISED FEBRUARY 1992

NE555, SA555, SE555, SE555C

PRECISION TIMERS

POST OFFICE BOX 655303

11

APPLICATION INFORMATION

C – Capacitance –

µF

100 k

10 k

1 k

100

10

1

100

10

1

0.1

0.01

0.1

0.001

tH + 0.693 (RA ) RB) C

tL + 0.693 (RB) C

Other useful relationships are shown below.

period

+ t

H ) tL + 0.693 (RA ) 2RB)C

frequency

[

1.44

(R

A )

2RB)C

Output driver duty cycle

+

tL

tH ) tL

+

RB

R

A )

2RB

Output waveform duty cycle

+

tH

tH ) tL

+ 1 *

RB

R

A )

2RB

Low t high ratio

+

tL

tH

+

RB

R

A )

RB

- o-

RA + 2 RB = 10 MΩ

RA + 2 RB = 1 MΩ

RA + 2 RB = 100 kΩ

RA + 2 RB = 10 kΩ

RA + 2 RB = 1 kΩ

Figure 14. Free-Running Frequency

missing-pulse detector

The circuit shown in Figure 15 may be used to detect a missing pulse or abnormally long spacing between

consecutive pulses in a train of pulses. The timing interval of the monostable circuit is continuously retriggered

by the input pulse train as long as the pulse spacing is less than the timing interval. A longer pulse spacing,

missing pulse, or terminated pulse train permits the timing interval to be completed, thereby generating an

output pulse as illustrated in Figure 16.

Time – 0.1 ms/div

VCC = 5 V

RA = 1 kΩ

C = 0.1

µF

See Figure 15

Capacitor Voltage

Output Voltage

Input Voltage

VCC (5 V to 15 V)

DISCH

OUT

VCC

RESET

RL

RA

A5T3644

C

THRES

GND

CONT

TRIG

Input

0.01

Output

48

3

7

6

2

5

1

Pin numbers shown are shown for the D, JG, and P packages.

Figure 15. Circuit for Missing-Pulse Detector

Figure 16. Missing-Pulse Detector Waveform