LMV358MM datasheet(19/27 Pages) NSC

19 / 27 page

Application Notes (Continued)

When the output voltage V

O is first at its high, VOH, the

capacitor C is charged toward V

OH through R2. The voltage

across C rises exponentially with a time constant

τ =R

2C,

and this voltage is applied to the inverting input of the op

amp. Meanwhile, the voltage at the non-inverting input is set

at the positive threshold voltage (V

TH+) of the generator. The

capacitor voltage continually increases until it reaches V

TH+,

at which point the output of the generator will switch to its

low, V

OL (= 0V in this case). The voltage at the non-inverting

input is switched to the negative threshold voltage (V

TH-)of

the generator. The capacitor then starts to discharge toward

OL exponentially through R1, with a time constant

τ =R

1C.

When the capacitor voltage reaches V

TH-, the output of the

pulse generator switches to V

OH. The capacitor starts to

charge, and the cycle repeats itself.

As shown in the waveforms in Figure 17, the pulse width (T

is set by R

2, C and VOH, and the time between pulses (T2)is

set by R

1, C and VOL. This pulse generator can be made to

have different frequencies and pulse width by selecting dif-

ferent capacitor value and resistor values.

Figure 18 shows another pulse generator, with separate

charge and discharge paths. The capacitor is charged

through R

1 and is discharged through R2.

Figure 19 is a squarewave generator with the same path for

charging and discharging the capacitor.

10006081

FIGURE 16. Pulse Generator

10006086

FIGURE 17. Waveforms of the Circuit in Figure 16

10006077

FIGURE 18. Pulse Generator

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