MC912DG128A Motorola, MC912DG128A Datasheet - Page 381

• Manufacturer Part Number: MC912DG128A
• Description: Microcontrollers
• Manufacturer: Motorola

Filter Components
Selection Guide
Equations Set
5-cgmpa
MOTOROLA
These equations can be used to select a set of filter components. Two
cases are considered:
In both equations, the power supply should be 5V. Start with the target
loop bandwidth as a function of the other parameters, but obviously,
nothing prevents the user from starting with the capacitor value for
example. Also, remember that the smoothing capacitor is always
assumed to be one tenth of the series capacitance value.
So with:
m:
R:
C:
F
F
for the ‘tracking’ mode:
and for the ‘acquisition’ mode:
:
bus
c
1. The ‘tracking’ mode. This situation is reached normally when the
2. The ‘acquisition’ mode. This situation is reached when the PLL
:
: the target bus frequency expressed in MHz
PLL operates in automatic bandwidth selection mode (AUTO=1 in
the PLLCR register).
operates in manual bandwidth selection mode and forced
acquisition (AUTO=0, ACQ=0 in the PLLCR register).
the multiplying factor for the reference frequency (i.e. (synr+1))
the series resistance of the low pass filter in
the series capacitance of the low pass filter in nF
the desired damping factor
the desired loop bandwidth expressed in Hz
Appendix B: CGM Practical Aspects
F
F
c
c
=
=
2 10
------------------------ -
2 10
------------------------ -
R C
R C
9
9
2
2
=
=
415.61 e
-------------------------------------------------------- -
37.78 e
----------------------------------------------------- -
Practical Aspects For The PLL Usage
2
2
Appendix B: CGM Practical Aspects
1.675 F
---------------------------- -
1.675 F
---------------------------- -
10.795
10.795
m
m
–
–
MC68HC912DT128A Rev 2.0
bus
bus
R
R
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