TDA5250D2_07 Datasheet, PDF (56/94 Pages) Infineon Technologies AG – ASK/FSK 868MHz Wireless Transceiver

TDA5250 D2
Version 1.7
Application
3.2.3 Parasitics
For the correct calculation of the external capacitors the parasitic capacitances of the pins and the
switches (C₂₀, C₂₁, C₂₂) have to be taken into account.
XOUT 19
L
-R
f, C_L
XIN 21
C_V1
XSWF 20
XSWA 22
C_V2
C_V3
XGND 23
C₂₁
C_tune1
C₂₂
C₂₀
C_tune2
Figure 3-19 parasitics of the switching network
QOSC_parasitics.wmf
Table 3-2
Typical values of parasitic capacitances
Name
Value
C20
4,5 pF
C21
FSK-: 2,8 pF / FSK+&ASK: 2.3pF
C22
1,3 pF
With the given parasitics the actual C_v can be calculated:
Cv- = Cv1 + Ctune1 + C21
Cv+
=
-⁽--C----v----1----+-----C----t--u----n---e---1----⁾---^â‹---⁽---C----v---2-----+-----C----2---0-----+-----C----t--u---n----e---2---⁾-
Cv1
+
Ct
un
e1
+
Cv2
+
C20
+
C
tu
ne
2
+
C21
Cvm
=
-⁽--C----v----1----+-----C----t--u----n---e---1----⁾---^â‹---⁽---C----v---2-----+-----C----2---0-----+-----C----v---3-----+-----C----2---2----+-----C----t---u---n----e---2---⁾-
Cv
1
+
Ctu
n
e1
+
Cv
2
+
C20
+
C
v3
+
C22
+
C
tu
ne
2
+
C21
[3 – 24]
[3 – 26]
Data Sheet
56
2007-02-26