XR-2209 Datasheet, PDF (13/20 Pages) Exar Corporation – Voltage-Controlled Oscillator

XR-2209
If R = 2MW, R_C = 2kW, 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:
frequency is given as:
ƪ ǒ Ǔƫ f
+
1
RC
1
)
R
R_C
1
–
V_C
V_T
K
+
Df
DV_C
+
-
1
RCCV_EE
HzńV
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.
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:
ǒ Ǔ V_C + V_T
1
)
R_C
R
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
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
V_CC
C
1mF
R_L
12
V_CC TC1
3
TC2 _SWO ⁷
XR-2209
8
TWO
5
BIAS
Square Wave
Output
Triangle Wave
Output
T4
4
I_T
V_EE
6
V_EE
I_O
I_C
R
R_C
1mF
V_C
V_C-
V_EE
V_C+ _Sweep
or
FM
Voltage
Figure 15. Frequency Sweep Operation, Split Supply
Rev. 2.02
13