XR-2209
Rev. 2.02
13
If R = 2M, R
C
= 2k, C = 5000pF, then a 1000:1
frequency sweep would result for a negative sweep
voltage V
C
V
EE
.
The voltage to frequency conversion gain, K, is controlled
by the series resistance RC and can be expressed as:
K
+
f
V
C
+
-
1
R
C
CV
EE
Hz
ń
V
The circuit of
Figure 15
can operate both with positive
and negative values of control voltage. However, for
positive values of V
C
with small (R
C
/R) ratio, the direction
of the timing current I
T
is reversed and the oscillations will
stop.
Frequency Control (Sweep and FM) - Single Supply
The circuit given in
Figure 16
shows the frequency sweep
method for single supply operation. Here, the oscillation
frequency is given as:
f
+
1
RC
ƪ
1 )
R
R
C
ǒ
1
–
V
C
V
T
Ǔ
ƫ
where V
T
= Vpin4 ~ Vbias + 0.7V.
This equation is valid from V
C
= 0V where R
C
is in parallel
with R and I
T
is maximum to:
V
C
+
V
T
ǒ
1 )
R
C
R
Ǔ
where I
T
= 0 and oscillation ceases.
Caution: Total timing current I
T
must be less than 6mA over the
frequency control range.
V
CC
R
L
Square Wave
Output
V
CC
Triangle Wave
C
V
CC
1F
4
6
BIAS
5
TWO
8
SWO
7
TC2
3
TC1
21
XR-2209
R
R
C
V
C
+
V
C
I
T
I
C
I
O
Output
1F
V
C
-
Sweep
or
FM
Voltage
Figure 15. Frequency Sweep Operation, Split Supply
V
EE
V
EE
V
EE
T4
