MC1455, MC1455B, NCV1455B

http://onsemi.com

8

Pulse Width Modulation

If the timer is triggered with a continuous pulse train in the

monostable mode of operation, the charge time of the

capacitor can be varied by changing the control voltage at

Pin 5. In this manner, the output pulse width can be

modulated by applying a modulating signal that controls the

threshold voltage.

Figure 24. Pulse Width Modulator

Output

Clock

Input

Modulation

Input

C

7

6

5

48

3

2

1

MC1455

t = 0.5 ms/cm

Figure 25. Pulse Width Modulation Waveforms

Test Sequences

Several timers can be connected to drive each other for

sequential timing. An example is shown in Figure 26 where

the sequence is started by triggering the first timer which

runs for 10 ms. The output then switches low momentarily

and starts the second timer which runs for 50 ms and so forth.

Figure 26. Sequential Timer

Load

MC1455

6

7

2

84

5

3

27 k

1

5.0

mF

Load

MC1455

9.1 k

6

7

1.0

mF

2

84

5

3

0.01

mF

27 k

1

0.001

mF

5.0

mF

MC1455

6

7

2

84

5

3

1

Load

0.001

mF

18.2 k

9.1 k

0.01

mF

0.01

mF