mc145170-2 Freescale Semiconductor, Inc, mc145170-2 Datasheet - Page 19

• Manufacturer Part Number: mc145170-2
• Description: Pll Frequency Synthesizer With Serial Interface
• Manufacturer: Freescale Semiconductor, Inc

Power is dissipated in the effective series resistance of the crystal, R
level specified by the crystal manufacturer represents the maximum stress that the crystal can withstand
without damage or excessive shift in operating frequency. R1 in
of R1 is not necessary in most cases.
To verify that the maximum dc supply voltage does not cause the crystal to be overdriven, monitor the
output frequency at the REF
frequency should increase very slightly as the dc supply voltage is increased. An overdriven crystal
decreases in frequency or becomes unstable with an increase in supply voltage. The operating supply
voltage must be reduced or R1 must be increased in value if the overdriven condition exists. The user
should note that the oscillator start-up time is proportional to the value of R1.
Through the process of supplying crystals for use with CMOS inverters, many crystal manufacturers have
developed expertise in CMOS oscillator design with crystals. Discussions with such manufacturers can
prove very helpful.
Freescale Semiconductor
Figure 21. Parasitic Capacitances of the Amplifier and C
out
NOTE: Values are supplied by crystal manufacturer (parallel resonant crystal).
1
pin (OSC
Figure 20. Pierce Crystal Oscillator Circuit
OSC
Figure 22. Equivalent Crystal Networks
in
5.0 to 10 pF
* May be needed in certain cases. See text.
MC145170-2 Technical Data, Rev. 5
out
C1
2
C
in
is not used because loading impacts the oscillator). The
OSC
in
1
1
C
R
f
stray
C2
C
Re
RS
R1*
a
OSC
Xe
Synthesizer
CO
Frequency
C
LS
out
out
Figure 20
2
CS
e
, in
OSC
Figure
out
limits the drive level. The use
2
stray
22. The maximum drive
Design Considerations
19