CY28439 SpectraLinear, CY28439 Datasheet - Page 10

• Manufacturer Part Number: CY28439
• Description: Clock Generator
• Manufacturer: SpectraLinear

Rev 1.0, November 21, 2006
Byte 15: Control Register 15 (continued)
Byte 16: Control Register 16
The CY28439 requires a Parallel Resonance Crystal. Substi-
tuting a series resonance crystal will cause the CY28439 to
operate at the wrong frequency and violate the ppm specifi-
cation. 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 configuration using the two
trim capacitors. An important clarification for the following
discussion is that the trim capacitors are in series with the
Table 4. Crystal Recommendations
14.31818 MHz
Frequency
Bit
Bit
2
1
0
7
6
5
4
3
2
1
0
(Fund)
@Pup
@Pup
0
0
0
1
1
0
0
0
0
0
0
Cut
AT
Watchdog Autorecovery Watchdog Autorecovery Mode
Loading Load Cap
Parallel
SRC_FREQ_SEL
Prog_SRC_EN
Prog_CPU_EN
Recovery N2
Recovery N1
Recovery N0
RESERVED
SRC_SATA
USB48
Name
Name
REF1
20 pF
0.1 mW
Watchdog Recovery Bit
Watchdog Recovery Bit
Watchdog Recovery Bit
REF1 Output Enable
0 = Disable, 1 = Enable
USB48 Output Enable
0 = Disable, 1 = Enable
SRC Frequency selection
0: SRC frequency is selected via the FS_E pin
1: SRC frequency is initially set to 167 MHz.
RESERVED
SATA PLL Spread Spectrum Enable
0 = Spread off, 1 = Spread on
Programmable SRC frequency enable
0 = disabled, 1 = enabled.
Programmable CPU frequency enable
0 = disabled, 1 = enabled.
0 = Disable (Manual), 1= Enable (Auto)
(max.)
Drive
Shunt Cap
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 capacitance of the crystal.
This is not true.
(max.)
5 pF
Figure 2. Crystal Capacitive Clarification
Motional
0.016 pF
(max.)
Description
Description
Tolerance
35 ppm
(max.)
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Stability
30 ppm
(max.)
CY28439
Page 10 of 21
(max.)
Aging
5 ppm