CY28446
Byte 8: Control Register 7
Bit
7
@Pup
Name
Description
0
1
Reserved
SRC[T/C]10
Reserved set to 0
6
SRC[T/C]10 Output Enable
0 = Disable (Tri-state), 1 = Enable
5
4
1
1
SRC[T/C]9
SRC[T/C]8
SRC[T/C]9 Output Enable
0 = Disable (Tri-state), 1 = Enable
SRC[T/C]8 Output Enable
0 = Disable (Tri-state), 1 = Enable
3
2
0
0
Reserved
SRC10
Reserved set to 0
Allow control of SRC[T/C]10 with assertion of OEA#
0 = Free running, 1 = Stopped with OEA#
1
0
0
0
SRC9
SRC8
Allow control of SRC[T/C]9 with assertion of OEB#
0 = Free running, 1 = Stopped with OEB#
Allow control of SRC[T/C]8 with assertion of OEA#
0 = Free running, 1 = Stopped with OEA#
Byte 9: Control Register 8
Bit
@Pup
Name
Description
7
0
PCI3
33-MHz Output drive strength
0 = Low, 1 = High
6
5
4
3
0
0
0
0
PCI2
PCI1
33-MHz Output drive strength
0 = Low, 1 = High
33-MHz Output drive strength
0 = Low, 1 = High
PCI0
33-MHz Output drive strength
0 = Low, 1 = High
PCIF0
33-MHz Output drive strength
0 = Low, 1 = High
2
1
0
1
1
1
Reserved
Reserved
Reserved
Reserved set to 1
Reserved set to 1
Reserved set to 1
.
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
The CY28446 requires a Parallel Resonance Crystal. Substi-
tuting a series resonance crystal causes the CY28446 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, use the total capac-
itance the crystal sees to calculate the appropriate capacitive
loading (CL).
Figure 1. Crystal Capacitive Clarification
Figure 1 shows a typical crystal configuration using the two
trim capacitors. It is important that the trim capacitors are in
series with the crystal. It is not true that load capacitors are in
parallel with the crystal and are approximately equal to the
load capacitance of the crystal.
Calculating Load Capacitors
In addition to the standard external trim capacitors, consider
the trace capacitance and pin capacitance to calculate the
crystal loading correctly. Again, the capacitance on each side
Rev 1.0,November 20, 2006
Page 8 of 19
SPECTRALINEAR [ SPECTRALINEAR INC ]
