mc68hc912dg128 Freescale Semiconductor, Inc, mc68hc912dg128 Datasheet - Page 411

• Manufacturer Part Number: mc68hc912dg128
• Description: M68hc12 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

20.4.3 Filter Components Selection Guide
20.4.3.1 Equations Set
MC68HC912DG128 — Rev 3.0
MOTOROLA
feature even in manual bandwidth control, offering then to the
application software the same flexibility for the clocking control as the
automatic mode.
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:
:
bus
c
1. The ‘tracking’ mode. This situation is reached normally when the
2. The ‘acquisition’ mode. This situation is reached when the PLL
:
Freescale Semiconductor, Inc.
: the target bus frequency expressed in MHz
For More Information On This Product,
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: CGM Practical Aspects
Go to: www.freescale.com
F
c
=
2 10
------------------------ -
R C
9
2
=
37.78 e
----------------------------------------------------- -
Practical Aspects For The PLL Usage
2
1.675 F
---------------------------- -
Appendix: CGM Practical Aspects
10.795
m
–
bus
R
Technical Data
411