CY28439
Byte 15: Control Register 15 (continued)
Bit
2
@Pup
Name
Description
0
0
0
Recovery N2
Recovery N1
Recovery N0
Watchdog Recovery Bit
Watchdog Recovery Bit
Watchdog Recovery Bit
1
0
Byte 16: Control Register 16
Bit
@Pup
Name
Description
7
1
REF1
REF1 Output Enable
0 = Disable, 1 = Enable
6
5
1
0
USB48
USB48 Output Enable
0 = Disable, 1 = Enable
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
3
0
0
RESERVED
SRC_SATA
RESERVED
SATA PLL Spread Spectrum Enable
0 = Spread off, 1 = Spread on
2
1
0
0
0
0
Prog_SRC_EN
Prog_CPU_EN
Programmable SRC frequency enable
0 = disabled, 1 = enabled.
Programmable CPU frequency enable
0 = disabled, 1 = enabled.
Watchdog Autorecovery Watchdog Autorecovery Mode
0 = Disable (Manual), 1= Enable (Auto)
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 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.
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
Figure 2. Crystal Capacitive Clarification
Table 4. Crystal Recommendations
Frequency
(Fund)
Drive
(max.)
Shunt Cap Motional
(max.)
Tolerance
(max.)
Stability
(max.)
Aging
(max.)
Cut
Loading Load Cap
Parallel 20 pF
(max.)
14.31818 MHz
AT
0.1 mW
5 pF
0.016 pF
35 ppm
30 ppm
5 ppm
Rev 1.0,November 21, 2006
Page 10 of 21
SPECTRALINEAR [ SPECTRALINEAR INC ]
