tda5255e1 Infineon Technologies Corporation, tda5255e1 Datasheet - Page 50

• Manufacturer Part Number: tda5255e1
• Description: Ask/fsk 434mhz Wireless Transceiver
• Manufacturer: Infineon Technologies Corporation

Confidential
Figure 3-15
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
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.
Preliminary Specification
C
L
=
C L ±
C
1
V
-
Crystal Oscillator
w
1
=
2
L
C L
----------------------------------------------------------------------------------------- -
OSC
C
w:
L
C
C
C
f:
N:
Df:
OSC
1
L
L
0
1
+ -
:
:
:
:
±
«
C 0
N f ×
----------
:
Df
C
×
V
N f ×
----------
Df
-R
×
=
æ
ç
è
crystal load capacitance for nominal frequency
angular frequency
inductivity of the crystal oscillator - typ: 2.7mH with pad of board
crystal load capacitance for nominal frequency
shunt capacitance of the crystal
motional capacitance of the crystal
crystal oscillator frequency
division ratio of the PLL
peak frequency deviation
1
C
×
1
+
æ
ç
è
L
1
2
---------------------------------
+
+
×
w
(
1
2
---------------------------------
C 0
2
TDA 5250
×
C 1
L
(
L
OSC
C 0
+
OSC
C
C L
1
+
C L
)
ö
÷
ø
)
50
ö
÷
ø
f, C
v
.
L
C
V
2.45µH without pad
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TDA5255 E1
Version 1.1
Application
2002-11-28
QOSZ_NIC.wmf