LMX9814 National Semiconductor, LMX9814 Datasheet - Page 2

• Manufacturer Part Number: LMX9814
• Manufacturer: National Semiconductor

Specifications of LMX9814

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4.0
Frequency Tuning is achieved by adjusting the crystal load
capacitance with external capacitors. It is a Bluetooth
requirement that the frequency is always within ±20 ppm.
So a crystal with an aging and temperature drift specifica-
tion of better than ±20 ppm is required. Here is an example:
The VXE4-1055 is a 12 MHz SMT crystal from Vite.
National is using this crystal with the LMX5251, LMX9814,
and LMX9820. Table 4-1 shows the specification of VXE4-
1055.
Since the internal capacitance of the crystal circuit is 4-5
pF and the load capacitance is 9 pF, 10 pF is a good start-
ing point for Ct1 and Ct2. The 2480 MHz RF frequency off-
set is then tested. Figure 4-1 shows the RF frequency
offset test results.
Figure 4-1 shows the results are 100 kHz off the center fre-
quency, which is –4 ppm. The pullability of the crystal is 24
ppm/pF, so the load capacitance must be decreased by
about 0.2 pF. By changing Ct1 or Ct2 to 9 pF, the total load
capacitance is increased by 0.26 pF. Figure 4-2 shows the
frequency offset test resuts. The frequency offset is now
zero with Ct1 = 9 pF, Ct2 = 10 pF.
Frequency Tuning
Figure 4-1. Frequency Offset with 10 pF Capacitors
2
Specification
Package
Frequency
Mode
Stability
Load Capacitance
ESR
Shunt Capacitance
Drive Level
Pullability
Storage Temperature
Table 4-1. VXE4-1055-12M000
Value
6x3.5x1.1 mm tall 4 pads
12.000 MHz
Fundamental
±18 ppm at -20 to +70°C
(inclusive of all conditions)
9 pF
40 Ω max, 20 Ω typ
7 pF max
10 to 100 µW
24 ppm/pF min
-40 to +85°C
(Confidential) Revision 1.0