Clock and Board Guidelines
MPC561/MPC563 Reference Manual, Rev. 1.2
C-6
Freescale Semiconductor
Figure C-6. RC Filter Example
Figure C-7. LC Filter Example (Alternative)
C.2.3
PLL Off-Chip Capacitor C
XFC
C
XFC
is the PLL feedback capacitor. It must be located as close as possible to the XFC and VDDSYN pads.
The maximum noise allowed on XFC is 50 mV peak-to-peak with a typical cut-off frequency of 500 Hz.
The XFC capacitor creates a low pass filter in the PLL loop. The filter output feeds the PLL VCO. The
capacitor is charged and discharged by short current pulses, generated by the phase detector. So the
capacitor leakage and absorption directly affect the AC component in the VCO input voltage that creates
PLL output clock jitter. Therefore, the dielectric quality of C
XFC
should be high.
Smaller C
XFC
makes the PLL faster to gain lock but less stable. Higher C
XFC
makes the PLL more stable
but slower to gain lock. Because each board layout and application is unique, C
XFC
must be evaluated in
a system.
The minimum required value (including capacitor tolerance) for C
XFC
is determined by the following two
cases:
0 < (MF+1) < 4
C
XFC
= (1130 * (MF+1) – 80) pF
(MF+1) >= 4
C
XFC
= (2100 * (MF+1)) pF
VDDSYN
VSSSYN
Keyed
100 nF
10
Ω
VDD 2.6 V
Board
MPC56x Device
Note: A filter cut off frequency of 500Hz is recommended, however this will result in a
capacitor size of 33uF using a 10 Ohm resistor. This may be too expensive or large
for the system. In this case the filter shown with cut- off frequency of 160kHz will suffice.
VDDSYN
VSSSYN
Keyed
100 nF
8.2 mH
VDD 2.6 V
Board
MPC56x Device
Note: A filter cut off frequency of 500Hz is recommended, however this will result in a
capacitor size of 15uF using a 8.2mH inductor. This may be too expensive or large
for the system. In this case the filter shown with cut- off frequency of 5.5kHz will suffice.
Summary of Contents for MPC561
Page 84: ...MPC561 MPC563 Reference Manual Rev 1 2 lxxxiv Freescale Semiconductor...
Page 144: ...Signal Descriptions MPC561 MPC563 Reference Manual Rev 1 2 2 46 Freescale Semiconductor...
Page 206: ...Central Processing Unit MPC561 MPC563 Reference Manual Rev 1 2 3 62 Freescale Semiconductor...
Page 302: ...Reset MPC561 MPC563 Reference Manual Rev 1 2 7 14 Freescale Semiconductor...
Page 854: ...Time Processor Unit 3 MPC561 MPC563 Reference Manual Rev 1 2 19 24 Freescale Semiconductor...
Page 968: ...Development Support MPC561 MPC563 Reference Manual Rev 1 2 23 54 Freescale Semiconductor...
Page 1144: ...Internal Memory Map MPC561 MPC563 Reference Manual Rev 1 2 B 34 Freescale Semiconductor...
Page 1212: ...TPU3 ROM Functions MPC561 MPC563 Reference Manual Rev 1 2 D 60 Freescale Semiconductor...
Page 1216: ...Memory Access Timing MPC561 MPC563 Reference Manual Rev 1 2 E 4 Freescale Semiconductor...
