TDA5255E1 Datasheet, PDF (50/93 Pages) Infineon Technologies AG – ASK/FSK 434MHz Wireless Transceiver

Confidential
TDA5255 E1
Version 1.1
Application
-R
L_OSC
f, C_L
C_V
TDA 5250
Figure 3-15 Crystal Oscillator
QOSZ_NIC.wmf
C_L
=
1
C_V
1
- w ² L_OSC
« C_V
=
1
C_L
1
+ w ² L_OSC
[3 – 17]
C_L:
w:
L_OSC:
crystal load capacitance for nominal frequency
angular frequency
inductivity of the crystal oscillator - typ: 2.7mH with pad of board
2.45µH without pad
With the aid of this formula it becomes obvious that the higher the serial capacitance C_V is, the
higher is the influence of L_OSC.
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.
In case of small frequency deviations (up to +/- 1000 ppm), the desired load capacitances for FSK
modulation are frequency depending and can be calculated with the formula below.
CL _±
= ^{C-----L-----+-}-----C----0----^×----N-----^{D------×--f----f-----×}---^èçæ---1----+-----2----------^{×------(----C--------C-0-------1--+----------C--------L--------)---ø÷ö}-
1
±
N---^D---×^-f--f-
×
æ
ç1
è
+
-2----^×---⁽--C----C-0---1-+-----C----L----⁾-_ø÷ö
[3 – 18]
C_L:
crystal load capacitance for nominal frequency
C₀:
shunt capacitance of the crystal
C₁:
motional capacitance of the crystal
f:
crystal oscillator frequency
N:
division ratio of the PLL
Df:
peak frequency deviation
Preliminary Specification
50
2002-11-28