Pll Wiring (Power Supply); Figure 53: Recommended For Pll Power Supply Filter - Siemens ERTEC 200P-2 Manual

4.3 PLL Wiring (Power Supply)

Since GND noise may affect VDD through C1 and C2, GND must be stable.

Figure 53: Recommended for PLL Power Supply Filter

Dimensioning the PLL Power Supply Filter
R R C C
L 1 2
( damping factor)
2 L
1
f (cut off frequency in Hz)
0
2 L ( C C )
1 2
where R+R 0.8 , C 10 µF, 0.7 (should not be less than 0.7 to decrease the
L 2
sensitivity for resonance), f <= 5kHz
0
Example:
With R+R = 0.8 , L = 22 µH, C = 68 µF, C = 0.3 µF (ceramic capacitor) this results in f
L 2 1 0
= 4.1 kHz and = 0.70.
C should be an SMD capacitor (e.g. ceramic 300 nF) for elimination of high frequency
1
components. Be sure to place it as close as possible to a power supply pin.
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