MC68HC912DG128A MOTOROLA [Motorola, Inc], MC68HC912DG128A Datasheet - Page 377

• Manufacturer Part Number: MC68HC912DG128A
• Description: microcontroller unit 16BIT DEVICE
• Manufacturer: MOTOROLA [Motorola, Inc]

1-cgmpa
MOTOROLA
Contents
Introduction
A Few Hints For The CGM Crystal Oscillator Application
What Loading
Capacitors To
Choose?
NOTE:
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377
A Few Hints For The CGM Crystal Oscillator Application . . . . . . . . . 377
Practical Aspects For The PLL Usage . . . . . . . . . . . . . . . . . . . . . . . 380
Printed Circuit Board Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385
This sections provides useful and practical pieces of information
concerning the implementation of the CGM module.
First, from small-signal analysis, it is known that relatively large values
for C1 and C2 have a positive impact on the phase margin. However, the
higher loading they represent decreases the loop gain. Alternatively,
small values for these capacitors will lead to higher open loop gain, but
as the frequency of oscillation approaches the parallel resonance, the
phase margin, and consequently the ability to start-up correctly, will
decrease. From this it is clear that relatively large capacitor values
(>33pF), are reserved for low frequency crystals in the MHz range.
Using the recommended loading capacitor CL value from the crystal
manufacturer is a good starting point. Taking into account unavoidable
strays, this equates to about (CL-2pF).
Appendix B: CGM Practical Aspects
Appendix B: CGM Practical Aspects
Appendix B: CGM Practical Aspects
MC68HC912DT128A Rev 2.0
377