LMX9820SB/NOPB National Semiconductor, LMX9820SB/NOPB Datasheet - Page 17

• Manufacturer Part Number: LMX9820SB/NOPB
• Manufacturer: National Semiconductor

Specifications of LMX9820SB/NOPB

• Lead Free Status / Rohs Status: Compliant

Revision 1.0
performance. Crystal load capacitance (C
the following:
C
The C
capacitance C0 as shown in Figure 11 on page 17, so the
total capacitance is:
C
2. Crystal Pullability
Pullability is another important parameter for a crystal,
which is the change in frequency of a crystal with units of
ppm/pF, either from the natural resonant frequency to a
load resonant frequency, or from one load resonant fre-
quency to another. The frequency can be pulled in a paral-
lel resonant circuit by changing the value of load
capacitance. A decrease in load capacitance causes an
increase in frequency, and an increase in load capacitance
causes a decrease in frequency.
3. Frequency Tuning
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.
Crystal/oscillator must have cumulative accuracy specifica-
tions of +15 ppm to provide margin for frequency drift with
ageing and temperature.
4. Vite Crystal
The VXE4-1055 is a 12 MHz SMT crystal from Vite.
National is using this crystal with the LMX9820. Table 21
on page 17 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 starting
point for both Ct1 and Ct2. The 2480 MHz RF frequency
offset is then tested. Figure 12 on page 18 shows the RF
frequency offset test results.
L
total
= C
= C
Figure 10. LMX9820 Crystal Recommended
L
int
above does not include the crystal internal self-
XTL_G
L
+ Ct1//Ct2
Figure 11. Crystal Equivalent Circuit
+ C0
Ct1
R1
Circuit
Crystal
C1
C0
L)
L1
is calculated as
XTL_D
Ct2
17
Figure 12 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 13 shows the
frequency offset test resuts. The frequency offset is now
zero with Ct1 = 9 pF, Ct2 = 10 pF.
5. Kinseki KSS CX-4025S
The LMX9820 has also been tested with the Kineski KSS
CX-4025S. See Table 22 on page 17.
Specification
Package
Frequency
Mode
Stability
Load Capacitance
ESR
Shunt Capacitance
Drive Level
Pullability
Storage Temperature
Specification
Package
Frequency
Mode
Stability
Load Capacitance
ESR
Shunt Capacitance
Drive Level
Storage Temperature
Table 21. VXE4-1055-12M000
Table 22. KSS CX-4025S
Value
6.0x3.5x1.1 mm - 4 pads
12.000 MHz
Fundamental
±18 ppm at -20 to +70°C (in-
clusive of all conditions)
9 pF
40
7 pF max
10 to 100 µW
24 ppm/pF min
-40 to +85°C
Value
4.0x2.5x0.75 mm - 4 pads
12.000 MHz
Fundamental
±20 ppm at -30 to +80°C (in-
clusive of all conditions)
12pF
80
3 pF max
100 µW max
-40 to +85°C
max, 20
max, 20
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