Datasheet

LMV331-N, LMV339-N, LMV393-N
SNOS018G –AUGUST 1999–REVISED FEBRUARY 2013 www.ti.com
(13)
Where V
max
is the max applied potential across the capacitor = (2V
CC
/3)
and V
C
= Vmax/2 = V
CC
/3
One period will be given by:
1/freq = 2t (14)
or calculating the exponential gives:
1/freq = 2(0.694) R
4
C
1
(15)
Resistors R
3
and R
4
must be at least two times larger than R
5
to insure that V
O
will go all the way up to V
CC
in
the high state. The frequency stability of this circuit should strictly be a function of the external components.
FREE RUNNING MULTIVIBRATOR
A simple yet very stable oscillator that generates a clock for slower digital systems can be obtained by using a
resonator as the feedback element. It is similar to the free running multivibrator, except that the positive feedback
is obtained through a quartz crystal. The circuit oscillates when the transmission through the crystal is at a
maximum, so the crystal in its series-resonant mode.
The value of R
1
and R
2
are equal so that the comparator will switch symmetrically about +V
CC
/2. The RC
constant of R
3
and C
1
is set to be several times greater than the period of the oscillating frequency, insuring a
50% duty cycle by maintaining a DC voltage at the inverting input equal to the absolute average of the output
waveform.
When specifying the crystal, be sure to order series resonant with the desired temperature coefficient.
Figure 17. Crystal controlled Oscillator
PULSE GENERATOR WITH VARIABLE DUTY CYCLE
The pulse generator with variable duty cycle is just a minor modification of the basic square wave generator.
Providing a separate charge and discharge path for capacitor C
1
generates a variable duty cycle. One path,
through R
2
and D
2
will charge the capacitor and set the pulse width (t
1
). The other path, R
1
and D
1
will discharge
the capacitor and set the time between pulses (t
2
).
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