cy28508 SpectraLinear Inc, cy28508 Datasheet - Page 7

• Manufacturer Part Number: cy28508
• Description: 333 Mhz Low-voltage Differential Sscg
• Manufacturer: SpectraLinear Inc

Rev 1.0, November 24, 2006
This circuitry is designed to present simultaneous M&N values
to the VCO when writing to the I
writing the N register value, the VCO would use a new N value
and an old M value and would go to an indeterminate
frequency until the next I
Crystal Recommendations
The CY28508 requires a Parallel Resonance Crystal.
Substituting a series resonance crystal will cause the
CY28508 to operate at the wrong frequency and violate the
ppm specification. For most applications there is a 300-ppm
frequency shift between series and parallel crystals due to
incorrect loading.
Crystal Loading
Crystal loading plays a critical role in achieving low ppm perfor-
mance. To realize low ppm performance, the total capacitance
the crystal will see must be considered to calculate the appro-
priate capacitive loading (CL). Figure 2 shows a typical crystal
Table 5. Crystal Recommendations
14.31818 MHz
Frequency
(Fund)
Cut
AT
Byte N1 W rite
2
Byte N0 W rite
Figure 1. Dial-a-Frequency Register Switching and Synchronizer Circuitry
C byte was written.
Loading Load Cap
Parallel
2
C lines. If not for this delay in
Byte M0 W rite
Byte M1 W rite
20 pF
FSEL
DAF-N0
DAF-N1
SMBus
SMBus
0.1 mW
(max.)
Drive
DAF-M1
DAF-M0
SMBus
SMBus
Latch
Latch
Shunt Cap
configuration using the two trim capacitors. An important clari-
fication for the following discussion is that the trim capacitors
are in series with the crystal not parallel. It’s a common
misconception that load capacitors are in parallel with the
crystal and should be approximately equal to the load capaci-
tance of the crystal.
(max.)
5 pF
Figure 2. Crystal Capacitive Clarification
Motional
0.016 pF
(max.)
Tolerance
50 ppm
(max.)
M Register
N Register
Stability
50 ppm
(max.)
CY28508
Page 7 of 13
(max.)
Aging
5 ppm