XR2209 datasheet(13/20 Pages) EXAR

13 / 20 page

XR-2209

Rev. 2.02

If R = 2M

W, RC = 2kW, C = 5000pF, then a 1000:1

frequency sweep would result for a negative sweep

voltage VC VEE.

The voltage to frequency conversion gain, K, is controlled

by the series resistance RC and can be expressed as:

+ Df

+ -

RCCV

Hz V

The circuit of

Figure 15 can operate both with positive

and negative values of control voltage. However, for

positive values of VC with small (RC/R) ratio, the direction

of the timing current IT 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:

+ 1

) R

–

where VT = Vpin4 ~ Vbias + 0.7V.

This equation is valid from VC = 0V where RC is in parallel

with R and IT is maximum to:

C + VT

)

where IT = 0 and oscillation ceases.

Caution: Total timing current IT must be less than 6mA over the

frequency control range.

VCC

Square Wave

Output

VCC

Triangle Wave

VCC

BIAS

TWO

SWO

TC2

TC1

XR-2209

VC+

Output

VC-

Sweep

Voltage

Figure 15. Frequency Sweep Operation, Split Supply

VEE

XR2209 Datasheet(PDF) 13 Page - Exar Corporation

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