TC1025 datasheet(6/16 Pages) MICROCHIP

6 / 16 page

TC1025

DS21656C-page 6

The frequency stability of this circuit should only be a

function of the external component tolerances.

Figure 4-5 shows the circuit for a pulse width modulator

circuit. It is essentially the same as in Figure 4-4, but

with the addition of an input control voltage. When the

input control voltage is equal to one-half VDD, operation

is basically the same as described for the free-running

oscillator. If the input control voltage is moved above or

below one-half VDD, the duty cycle of the output square

wave will be altered. This is because the addition of the

control voltage at the input has now altered the trip

points. The equations for these trip points are shown in

Figure 4-5 (see VH and VL). Pulse width sensitivity to

the input voltage variations can be increased by

reducing the value of R6 from 10k

Ω and conversely,

sensitivity will be reduced by increasing the value of

R6. The values of R1 and C1 can be varied to produce

the desired center frequency.

FIGURE 4-1:

COMPARATOR

EXTERNAL HYSTERESIS

CONFIGURATION

FIGURE 4-2:

32.768 kHz “TIME OF

DAY” CLOCK

OSCILLATOR

FIGURE 4-3:

NON-RETRIGGERABLE MULTIVIBRATOR

–

VDD

VOUT

VSRC

1/2

TC1025

VDD

VOUT

VDD

150k

100pF

32.768kHz

Vper = 30.52µsec

1/2

TC1025

–

VDD

CMPTR1

CMPTR2

OUT

562k

100k

10M

243k

10M

100pF

R10

61.9k

GND

VDD

GND

VDD

TC1025

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