MC68HC908GP20 Datasheet, PDF (138/406 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

filter capacitor, filter capacitor leakage, stray impedances on the circuit
board, and even humidity or circuit board contamination.
7.9.3 Choosing a Filter
As described in 7.9.2 Parametric Influences on Reaction Time, the
external filter network is critical to the 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 7-10 is recommended when using
a 32.768-kHz reference crystal. Figure 7-10 (a) is used for applications
requiring better stability. Figure 7-10 (b) is used in low-cost applications
where stability is not critical.
CGMXFC
CGMXFC
10 k
0.47 µF
0.01 µF
0.47 µF
V_SSA
(a)
V_SSA
(b)
Figure 7-10. PLL Filter
Advance Information
138
MC68HC908GP20 — Rev 2.1
Freescale Semiconductor