mc9s12xd256 Freescale Semiconductor, Inc, mc9s12xd256 Datasheet - Page 1270

• Manufacturer Part Number: mc9s12xd256
• Description: Hcs12x 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 grey boxes show the calculation for f
are used for f
The VCO gain at the desired VCO 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.
1270
ch
is the current in tracking mode.
1
, f
1
f
and i
osc
Phase Locked Loop
OSC
XFC Component Selection
ch
from
= 4-MHz and a 40-MHz bus clock.
K
refdv+1
V
C
1
Table
=
should be chosen to fulfill the Gardner’s stability criteria by at least a factor of 10,
K
K
1
A-23.
f
e
=
ref
--------------------------- -
f 1 f vco
Figure A-3. Basic PLL Functional Diagram
–
K 1 1V
V
i
DDPLL
–
ch
MC9S12XDP512 Data Sheet, Rev. 2.17
K
V
D
VCO
fcmp
=
C
–
p
C
=
= 80 MHz and f
3.5 A
s
Detector
–
Loop Divider
Phase
195MHz V
synr+1
KF
1
R
–
154MHz
e
ref
126 80
------------------- -
–
V
= 4 MHz. For example, these frequencies
195
XFC Pin
–
=
539.1Hz
1
2
= -154.0MHz/V
VCO
KV
Freescale Semiconductor
f
vco