tda5251f1 Infineon Technologies Corporation, tda5251f1 Datasheet - Page 48

• Manufacturer Part Number: tda5251f1
• Description: Ask/fsk 315mhz Wireless Transceiver
• Manufacturer: Infineon Technologies Corporation

Confidential
Choosing C L as large as possible results in a small pulling sensitivity. On the other hand a small C L
keeps the influence of the serial inductance and the tolerances associated to it small (see formula
[3-17]).
Start-up Time
The proportionality of L 1 and C 1 of the crystal is defined by formula [3-13]. For a crystal with a small
C 1 the start -up time will also be slower. Typically the lower the value of the crystal frequency, the
lower the C 1 .
A short conclusion regarding crystal and crystal oscillator dependencies is shown in the following
table:
Table 3-1
The crystal oscillator in the TDA5251 is a NIC (negative impedance converter) oscillator type. The
input impedance of this oscillator is a negative impedance in series to an inductance. Therefore the
load capacitance of the crystal C
capacitance C
Preliminary Specification
t
d
Independent variable
d
Start
frequency of quartz >
C
D
L
=
~
d
where:
f
d
-
L OSC >
S
C
´
C 1 >
C 0 >
C L >
R
L
f
Crystal and crystal oscilator dependency
v
S
L
-
as shown in formula [3-17].
1
=
R
2
ext
(
C
-R:
R
0
-
ext
+
C
:
C
1
L
)
2
is the negative impedance of the oscillator
see Figure 3-13
is the sum of all external resistances (e.g. R
other resistance that may be present in the circuit,
see Figure 3-12
Relative Tolerance Maximum Deviation
L
(specified by the crystal supplier) is transformed to the
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TDA5251 F1
t Start-up
Version 1.0
Application
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2003-02-18