FMPLL and crystal oscillator

AN4092

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Doc ID 023080 Rev 2

Figure 8.

Oscillator

2.1.1

External circuitry

The external circuitry normally consists of:

●

The crystal

●

Two load capacitors

●

Serial resistor (optional)

The bias resistor is not needed because it is internally implemented.

The maximum value of the total load capacitance is given by the following table:

Table 4.

The circuitry design may need also to take in account parasitic capacitance.

XTAL load capacitance

Min. (pF)

Max (pF)

4MHz

5

30

8MHz

5

26

12 MHz

5

23

16 MHz

5

19

20 MHz

5

16

40 MHz

5

8

l.

This value is determined by the crystal manufacturer and board design. For 4 MHz to 40 MHz crystals specified

for this PLL, load capacitors should not exceed these limits.