MC3456

8

MOTOROLA ANALOG IC DEVICE DATA

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 3. In this manner, the output pulse width can be

modulated by applying a modulating signal that controls the

threshold voltage.

Test Sequences

Several timers can be connected to drive each other for

sequential timing. An example is shown in Figure 24 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 22. Pulse Width Modulation Waveforms

Figure 23. Pulse Width Modulation Circuit

t = 0.5 ms/cm

(RA = 10 kW, C = 0.02 mF, VCC = 15 V)

+VCC (5.0 V to 15 V)

RL

4 (10)

Reset

VCC

14

RA

Discharge

1 (13)

Threshold

2 (12)

Control

3 (11)

C

Modulation

Input

Output

5 (9)

Trigger

6 (8)

Output

Clock

Input

Gnd

7

1/2

MC3456

Modulation Input Voltage 5.0 V/cm

Clock Input Voltage

5.0 V/cm

Output Voltage

5.0 V/cm

Capacitor Voltage

5.0 V/cm

Figure 24. Sequential Timing Circuit

9.1 k

Threshold

VCC

Reset

27 k

9.1 k

VCC

Reset

27 k

50 k

VCC

Reset

Control

Output

Load

Gnd

Gnd

Load

5.0

µF

0.001

µF

Gnd

Trigger

Discharge

1.0

µF

Control

Output

0.01

µF

0.001

µF

Threshold

Threshold

Discharge

Trigger

5.0

µF

0.01

µF

Discharge

Trigger

Load

VCC (5.0 V to 15 V)

0.01

µF

Control

Output

1/2

MC3456

1/2

MC3456

1/2

MC3456