TDA5252G2 Datasheet, PDF (48/86 Pages) Infineon Technologies AG – ASK/FSK 915MHz Wireless Transceiver

TDA5252 G2
Version 1.1
Application
Table 3-1 Crystal and crystal oscilator dependency
Result
Independent variable Relative Tolerance Maximum Deviation
C1 >
>>
>>
C0 >
<
<
frequency of quartz >
>>>
>
LOSC >
CL >
>>
>
>
<
t_Start-up
<
-
<<
-
-
The crystal oscillator in the TDA5252 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_L (specified by the crystal supplier) is transformed to the
capacitance C_v as shown in formula [3-17].
-R
L_OSC
f, C_L
C_V
TDA 5250
Figure 3-12 Crystal Oscillator
QOSZ_NIC.wmf
C_L
=
1
C_V
1
− ω ² L_OSC
↔ C_V
=
1
C_L
1
+ ω ² L_OSC
[3 – 17]
C_L:
ω:
L_OSC:
crystal load capacitance for nominal frequency
angular frequency
inductivity of the crystal oscillator - typ: 2.75µH with pad of board
2.5µH without pad
With the aid of this formula it becomes obvious that the higher the serial capacitance CV is, the
higher is the influence of LOSC.
The tolerance of the internal oscillator inductivity is much higher, so the inductivity is the dominating
value for the tolerance.
FSK modulation and tuning are achieved by a variation of C_v.
Data Sheet
48
2007-02-26