EL4584CSZ datasheet(9/15 Pages) RENESAS

9 / 15 page

EL4584

FN7174 Rev 3.00

Page 9 of 15

May 9, 2008

The resistance needed will depend on VCO design or VCXO

module selection.

Applications Information

Choosing External Components

1. To choose LC VCO components, first pick the desired

operating frequency. For our example, we will use

14.31818MHz, with an HSYNC frequency of 15.734kHz.

2. Choose a reasonable inductor value (10µH to 20µH

works well). We choose 15µH.

3. Calculate CT needed to produce FOSC, as shown in

Equations 1 and 2.

4. From the varactor data sheet find CV @ 2.5V, the desired

lock voltage. CV = 23pF for our SMV1204-12, for

example.

5. C2 should be about 10CV, so we choose C2 = 220pF for

our example.

6. Calculate C1 using Equations 3 and 4. Since:

then:

For our example, C1 = 14pF (a trim capacitor may be used

for fine tuning). Examples for each frequency using the

internal divider follow.

Typical Application

Horizontal genlock provides clock for an analog to digital

converter, digitizing analog video.

FIGURE 11.

FOSC

 LC

-----------------------

(EQ. 1)



2F2L

---------------------



2 14.318e6



2 15e 6

–



---------------------------------------------------------------------

8.2pF

(EQ. 2)

C1C2CV

C1C2



C1CV



C2CV



----------------------------------------------------------------------------

(EQ. 3)

C2CTCV

C2CV

 C

2CT



CTCV



–



--------------------------------------------------------------------------

(EQ. 4)

TABLE 3. LC VCO COMPONENT VALUES (APPROXIMATE)

(NOTE)

FREQUENCY

(MHZ)

(µH)

(pF)

13.301

220

13.5

220

14.75

220

17.734

220

10.738

220

12.273

220

14.318

220

NOTE: Use shielded inductors for optimum performance.

TABLE 4. XTAL VCO COMPONENT VALUES

(APPROXIMATE)

FREQUENCY

(MHz)

)

(pF)

(µF)

13.301

300

0.001

13.5

300

0.001

14.75

300

0.001

FIGURE 12. TYPICAL LC VCO

FIGURE 13. TYPICAL XTAL VCO

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