Datasheet

V
A2
=
V
CC
(R
2
||R
3
)
R
1
+ (R
2
||R
3)
V
A1
=
V
CC
.R
2
R
2
+ R
1
||R
3
C
1
= 750 pF
R
4
= 100 k:
V
O
R
2
= 100 k:
R
3
= 100 k:
R
1
= 100 k:
V
A
+
-
V
C
V
+
0
f |10 kHz
V
+
LMV7291
www.ti.com SNOSA86E –FEBRUARY 2004–REVISED MARCH 2013
Figure 31. Squarewave Oscillator
To analyze the circuit, consider it when the output is high. That implies that the inverted input (V
C
) is lower than
the non-inverting input (V
A
). This causes the C
1
to get charged through R
4,
and the voltage V
C
increases till it is
equal to the non-inverting input. The value of V
A
at this point is
(7)
If R
1
= R
2
= R
3
then V
A1
= 2V
CC
/3
At this point the comparator switches pulling down the output to the negative rail. The value of V
A
at this point is
(8)
If R
1
= R
2
= R
3
then V
A2
= V
CC
/3
The capacitor C
1
now discharges through R
4
, and the voltage V
C
decreases till it is equal to V
A2
, at which point
the comparator switches again, bringing it back to the initial stage. The time period is equal to twice the time it
takes to discharge C
1
from 2V
CC
/3 to V
CC
/3, which is given by R
4
C
1
.ln2. Hence the formula for the frequency is:
F = 1/(2.R
4
.C
1
.ln2)
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