MC9S12A128 Datasheet, PDF (76/92 Pages) Motorola, Inc – Microcontroller unit (MCU)

MC9S12A128 Device Guide — V01.01
A.5.3 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.5.3.1 XFC Component Selection
This section describes the selection of the XFC components to achieve a good filter characteristics.
V_DDPLL
C_s
C_p
R
f_osc
1
f_ref
refdv+1
Phase
∆
K_Φ
Detector
f_cmp
VCO
K_V
f_vco
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 i_ch from Table A-16.
The VCO Gain at the desired VCO output frequency is approximated by:
KV = K1 ⋅ e^{(---f--K1----1-–----⋅f--v-1--c-V---o----)}
The phase detector relationship is given by:
i_ch is the current in tracking mode.
K_Φ = – ich ⋅ KV
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