s908gz60cfa Freescale Semiconductor, Inc, s908gz60cfa Datasheet - Page 90

• Manufacturer Part Number: s908gz60cfa
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Clock Generator Module (CGM)
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.
4.8.3 Choosing a Filter
As described in
stability and reaction time of the PLL. The PLL is also dependent on reference frequency and supply
voltage.
Figure 4-9
the PLL are not critical, the three component filter network shown in
single capacitor, C
components at various reference frequencies. For reference frequencies between the values listed in the
table, extrapolate to the nearest common capacitor value. In general, a slightly larger capacitor provides
more stability at the expense of increased lock time.
90
shows two types of filter circuits. In low-cost applications, where stability and reaction time of
4.8.2 Parametric Influences on Reaction
F
1 MHz
2 MHz
3 MHz
4 MHz
5 MHz
6 MHz
7 MHz
8 MHz
f
MC68HC908GZ60 • MC68HC908GZ48 • MC68HC908GZ32 Data Sheet, Rev. 6
, as shown in shown in
RCLK
C
CGMXFC
F
Table 4-5. Example Filter Component Values
V
(A)
SSA
8.2 nF
4.7 nF
3.3 nF
2.2 nF
1.8 nF
1.5 nF
1.2 nF
1 nF
C
F1
Figure 4-9. PLL Filter
Figure 4-9
820 pF
470 pF
330 pF
220 pF
180 pF
150 pF
120 pF
100 pF
C
(A). Refer to
F2
Time, the external filter network is critical to the
C
R
F1
CGMXFC
F1
Table 4-5
R
Figure 4-9
2k
2k
2k
2k
2k
2k
2k
2k
(B)
F1
V
SSA
C
F2
for recommended filter
(B) can be replaced by a
6.8 nF
5.6 nF
4.7 nF
3.9 nF
3.3 nF
2.7 nF
2.2 nF
18 nF
C
Freescale Semiconductor
F