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t

H +

0.693 (R

A )

R

B)

C

t

L +

0.693 (R

B)

C

Other useful relationships are shown below.

period + tH ) tL + 0.693 (RA ) 2RB) C

frequency [

1.44

(R

A )

2R

B

) C

Output driver duty cycle +

t

L

t

H )

t

L

+

R

B

R

A )

2R

B

Output waveform duty cycle

+

t

L

t

H

+

R

B

R

A )

R

B

Low-to-high ratio

+

t

H

t

H )

t

L

+ 1–

R

B

R

A )

2R

B

C − Capacitance −

µF

100 k

10 k

1 k

100

10

1

100

10

1

0.1

0.01

0.1

0.001

Missing-Pulse Detector

Time − 0.1 ms/div

C = 0.1

µF

See Figure 15

Capacitor Voltage

Output Voltage

Input Voltage

DISCH

OUT

RESET

A5T3644

C

THRES

GND

CONT

TRIG

Input

0.01

Output

4

8

3

7

6

2

5

1

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

NA555, NE555, SA555, SE555

PRECISION TIMERS

SLFS022F – SEPTEMBER 1973 – REVISED JUNE 2006

APPLICATION INFORMATION (continued)

Figure 14. Free-Running Frequency

The circuit shown in Figure 15 can 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 retriggered continuously

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 shown in Figure 16.

Figure 15. Circuit for Missing-Pulse Detector

Figure 16. Completed Timing Waveforms for

Missing-Pulse Detector

11

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