PRELIMINARY
CY28439-2
Document #: 38-07750 Rev. *B
Page 10 of 22
The CY28439-2 requires a Parallel Resonance Crystal.
Substituting a series resonance crystal will cause the
CY28439-2 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 configuration using the two
trim capacitors. An important clarification 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 capacitance of the crystal.
This is not true.
2
0
Recovery N2
Watchdog Recovery Bit
1
0
Recovery N1
Watchdog Recovery Bit
0
0
Recovery N0
Watchdog Recovery Bit
Byte 16: Control Register 16
Bit
@Pup
Name
Description
7
1
REF1
REF1 Output Enable
0 = Disable, 1 = Enable
6
1
USB48
USB48 Output Enable
0 = Disable, 1 = Enable
5
0
SRC_FREQ_SEL
SRC Frequency selection
0: SRC frequency is selected via the FS_E pin
1: SRC frequency is initially set to 167 MHz.
4
0
RESERVED
RESERVED
3
0
SRC_SATA
SATA PLL Spread Spectrum Enable
0 = Spread off, 1 = Spread on
2
0
Prog_SRC_EN
Programmable SRC frequency enable
0 = disabled, 1 = enabled.
1
0
Prog_CPU_EN
Programmable CPU frequency enable
0 = disabled, 1 = enabled.
0
0
Watchdog Autorecovery Watchdog Autorecovery Mode
0 = Disable (Manual), 1= Enable (Auto)
Byte 15: Control Register 15 (continued)
Bit
@Pup
Name
Description
Figure 2. Crystal Capacitive Clarification
Table 4. Crystal Recommendations
Frequency
(Fund)
Cut
Loading Load Cap
Drive
(max.)
Shunt Cap
(max.)
Motional
(max.)
Tolerance
(max.)
Stability
(max.)
Aging
(max.)
14.31818 MHz
AT
Parallel
20 pF
0.1 mW
5 pF
0.016 pF
35 ppm
30 ppm
5 ppm
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