DOC#: SP-AP-0015 (Rev. 0.2) Page 2 of 11
Pin Definitions
The SL28SRC01 requires a Parallel Resonance Crystal.
Substituting a series resonance crystal causes the
SL28SRC01 to operate at the wrong frequency and violates
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, use the total capac-
itance the crystal sees to calculate the appropriate capacitive
loading (CL).
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
is in series with the crystal. The total capacitance on both side
is twice the specified crystal load capacitance (CL). Trim
Pin No.
Name Type Description
1 XIN I 14.318 MHz Crystal input.
2 VDD PWR 3.3V power supply
3 VDD PWR 3.3V power supply
4 VSS GND Ground
5 VDD PWR 3.3V power supply
6 VSS GND Ground
7 SRC1 O, DIF 100 MHz Differential serial reference clocks.
8 SRC1# O, DIF 100 MHz Differential serial reference clocks.
9 VSS GND Ground
10 VDD PWR 3.3V power supply
11 VDD PWR 3.3V power supply
12 VSS GND Ground
13 VDD PWR 3.3V power supply
14 SSON I 3.3V LVTTL input for enabling spread spectrum clock
0 = Disable, 1 = Enable (-0.5% SS)
Extrenal 10K ohm pull-up or pull-down resistor required
15 VSS GND Ground
16 XOUT O 14.318 MHz Crystal output.
Table 1. 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
Figure 1. Crystal Capacitive Clarification
