
Clock Generator Module (CGM)
MC68HC908AP Family Data Sheet, Rev. 4
96
Freescale Semiconductor
Temperature and processing also can affect acquisition time because the electrical characteristics of the
PLL change. The part operates as specified as long as these influences stay within the specified limits.
External factors, however, can cause drastic changes in the operation of the PLL. These factors include
noise injected into the PLL through the filter capacitor, filter capacitor leakage, stray impedances on the
circuit board, and even humidity or circuit board contamination.
6.8.3 Choosing a Filter
stability and reaction time of the PLL. The PLL is also dependent on reference frequency and supply
voltage.
Either of the filter networks in
Figure 6-10 is recommended when using a 32.768kHz reference clock
low-cost applications where stability is not critical.
Figure 6-10. PLL Filter
1 k
10 nF
0.22
F
VSSA
0.22
F
VSSA
(a)
(b)
CGMXFC