mc9s12hz256v2 Freescale Semiconductor, Inc, mc9s12hz256v2 Datasheet - Page 644

• Manufacturer Part Number: mc9s12hz256v2
• Description: Hcs12 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Appendix A Electrical Characteristics
A.5.3
The oscillator provides the reference clock for the PLL. The PLL´s Voltage Controlled Oscillator (VCO)
is also the system clock source in self clock mode.
A.5.3.1
This section describes the selection of the XFC components to achieve a good filter characteristics.
The following procedure can be used to calculate the resistance and capacitance values using typical values
for K
The VCO Gain at the desired VCO output frequency is approximated by:
The phase detector relationship is given by:
i
The loop bandwidth f
typical values are 50. = 0.9 ensures a good transient response.
644
K
K
ch
V
is the current in tracking mode.
1
=
=
, f
1
K
i
ch
and i
1
Phase Locked Loop
XFC Component Selection
e
K
ch
---------------------- -
V
f
K
from
1
f
1
osc
–
f
C
1V
vco
Table
should be chosen to fulfill the Gardner’s stability criteria by at least a factor of 10,
refdv+1
A-17.
1
Figure A-3. Basic PLL Functional Diagram
MC9S12HZ256 Data Sheet, Rev. 2.05
f
ref
f
cmp
Loop Divider
Detector
Phase
synr+1
K
1
C
s
VDDPLL
R
1
2
C
p
VCO
K
V
Freescale Semiconductor
f
vco