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MPC92429 REVISION 3 DECEMBER 14, 2012
9
2012 Integrated Device Technology, Inc.
MPC92429 Data Sheet
400 MHz Low Voltage PECL Clock Synthesizer
the crystal to ensure a stable, jitter free interface between the
crystal and the on-board oscillator. Although the MPC92429
has several design features to minimize the susceptibility to
power supply noise (isolated power and grounds and fully
differential PLL), there still may be applications in which
overall performance is being degraded due to system power
supply noise. The power supply filter and bypass schemes
discussed in this section should be adequate to eliminate
power supply noise related problems in most designs.
Figure 6. PCB Board Layout Recommendation
for the PLCC28 Package
The On-Chip Crystal Oscillator
The MPC92429 features an integrated on-chip crystal
oscillator to minimize system implementation cost. The
integrated oscillator is a Pierce-type that uses the crystal in
its parallel resonance mode. It is recommended to use a 10
to 20 MHz crystal with a load specification of CL = 10 pF.
Crystals with a load specification of CL = 20 pF may be used
at the expense of an slightly higher frequency than specified
for the crystal. Externally connected capacitors on both the
XTAL_IN and XTAL_OUT pins are not required but can be
used to fine-tune the crystal frequency as desired.
The crystal, the trace and optional capacitors should be
placed on the board as close as possible to the MPC92429
XTAL_IN and XTAL_OUT pins to reduce crosstalk of active
signals into the oscillator. Short and wide traces further
reduce parasitic inductance and resistance. It is further
recommended to guard the crystal circuit by placing a ground
ring around the traces and oscillator components. See
Table 11 for recommended crystal specifications.
As an alternative to parallel resonance mode crystals, the
oscillator also works with crystals specified in the series
resonance mode. With series resonance crystals, the
oscillator frequency and the synthesized output frequency of
the MPC92429 will be a approximately 350-400 ppm higher
than using crystals specified for parallel frequency mode.
This is applicable to applications using the MPC92429 in
sockets designed for the pin and function compatible
MC12429 synthesizer, which has an oscillator using the
crystal in its series resonance mode.
Table 12 shows the
recommended specifications for series resonance mode
crystals.
1
C2
CF
XTAL
C1
= VCC
= GND
= Via
Table 11. Recommended Crystal Specifications
Parameter
Value
Crystal Cut
Fundamental AT Cut
Resonance Mode
Parallel
Crystal Frequency
10–20 MHz
Shunt Capacitance C0
5–7 pF
Load Capacitance CL
10 pF
Equivalent Series Resistance ESR
20–60
Table 12. Alternative Crystal Specifications
Parameter
Value
Crystal Cut
Fundamental AT Cut
Resonance Mode
Series
Crystal Frequency
10–20 MHz
Shunt Capacitance C0
5–7 pF
Equivalent Series Resistance ESR
50–80