CY28416
Byte 7: Vendor ID
Bit @Pup
Name
Revision Code Bit 3
Revision Code Bit 2
Revision Code Bit 1
Revision Code Bit 0
Vendor ID Bit 3
Description
7
6
5
4
3
2
1
0
0
0
0
1
1
0
0
0
Revision Code Bit 3
Revision Code Bit 2
Revision Code Bit 1
Revision Code Bit 0
Vendor ID Bit 3
Vendor ID Bit 2
Vendor ID Bit 2
Vendor ID Bit 1
Vendor ID Bit 1
Vendor ID Bit 0
Vendor ID Bit 0
Table 5. Crystal Recommendations
Frequency
Drive
(max.)
Shunt Cap Motional
(max.)
Tolerance
(max.)
Stability
(max.)
Aging
(max.)
(Fund)
Cut
Loading Load Cap
(max.)
14.31818 MHz
AT
Parallel 20 pF
0.1 mW
5 pF
0.016 pF
50 ppm
50 ppm
5 ppm
(CL). While the capacitance on each side of the crystal is in
series with the crystal, trim capacitors (Ce1,Ce2) should be
calculated to provide equal capacitive loading on both sides.
Crystal Recommendations
The CY28416 requires a Parallel Resonance Crystal.
Substituting a series resonance crystal will cause the
CY28416 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.
Clock Chip
Ci2
Ci1
Pin
3 to 6p
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).
X2
X1
Cs2
Cs1
Figure 1 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.
Trace
2.8pF
XTAL
Ce1
Ce2
Trim
33pF
This is not true.
.
Figure 2. Crystal Loading Example
Use the following formulas to calculate the trim capacitor
values for Ce1 and Ce2.
Load Capacitance (each side)
Ce = 2 * CL – (Cs + Ci)
Total Capacitance (as seen by the crystal)
1
CLe
=
1
Ce2 + Cs2 + Ci2
1
Ce1 + Cs1 + Ci1
(
)
+
Figure 1. Crystal Capacitive Clarification
CL....................................................Crystal load capacitance
Calculating Load Capacitors
CLe......................................... Actual loading seen by crystal
using standard value trim capacitors
In addition to the standard external trim capacitors, trace
capacitance and pin capacitance must also be considered to
correctly calculate crystal loading. As mentioned previously,
the capacitance on each side of the crystal is in series with the
crystal. This means the total capacitance on each side of the
crystal must be twice the specified crystal load capacitance
Ce..................................................... External trim capacitors
Cs..............................................Stray capacitance (terraced)
Ci ...........................................................Internal capacitance
(lead frame, bond wires etc.)
Rev 1.0,November 22, 2006
Page 7 of 14
SPECTRALINEAR [ SPECTRALINEAR INC ]
