STV0684 datasheet(44/49 Pages) STMICROELECTRONICS

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Electrical Characteristics

STV0684

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4.7

External circuits

4.7.1

Crystal oscillator

There are 2 crystal oscillator pins XTAL_IN, XTAL_OUT, as shown in Figure 23. The Oscillator cell

architecture is a single stage oscillator with an inverter working as an amplifier. The oscillator stage

is biased by an internal resistor (>1M

Ω). It also requires an external PI network consisting of a

crystal and two capacitors.

Note:

The TV standards requests that the clock accuracy of the oscillator circuit must be 30ppm or less to

achieve a 500Hz accuracy for 4.5MHz chroma.

4.7.2

Audio

If the record audio section of the STV0684 is not required, AP, CBS, VC and AN can be left

unconnected. Power must still be supplied to VDDA and VDDAP.

4.7.3

Recommended power supply decoupling

A 0.1

µF bypass capacitor located as close as possible to the chip package connecting between all VDD pins

and GND and at least one bulk decoupling capacitor on each of the supply rails VDDA, VDDC, VDDI and

VDDP.

Figure 23: Oscillator support circuit

Figure 24: Audio PLL filter and CBS

XTALI

XTALO

Crystal

22pF

10µF

680pF

CBS

10K

10nF

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