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MC9S12C Datasheet, PDF (656/680 Pages) Motorola, Inc – 16-Bit Microcontroller | |||
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Appendix A Electrical Characteristics
A.4.3 Phase Locked Loop
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.4.3.1 XFC Component Selection
This section describes the selection of the XFC components to achieve a good ï¬lter characteristics.
Cp
VDDPLL
R
Cs
XFC Pin
Phase
VCO
fosc
1
fref
D
KF
refdv+1
fvco
KV
Detector
fcmp
Loop Divider
1
1
synr+1
2
Figure A-2. Basic PLL Functional Diagram
The following procedure can be used to calculate the resistance and capacitance values using typical values
for K1, f1 and ich from Table A-17.
The grey boxes show the calculation for fVCO = 50MHz and fref = 1MHz. E.g., these frequencies are used
for fOSC = 4MHz and a 25MHz bus clock.
The VCO Gain at the desired VCO frequency is approximated by:
KV = K1 â
e-(--fK--1--1--â--â
--f-1-v--c-V--o--=-) â100 â
e(---6---â0---1-â--0---50---0---=) -90.48MHz/V
The phase detector relationship is given by:
KΦ = â ich â
KV
ich is the current in tracking mode.
= 316.7Hz/â¦
656
MC9S12C-Family / MC9S12GC-Family
Freescale Semiconductor
Rev 01.23
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