TDA5251F1 Datasheet, PDF (53/88 Pages) Infineon Technologies AG – ASK/FSK 315MHz Wireless Transceiver

TDA5251 F1
Version 1.0
Confidential
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 3-17 parasitics of the switching network
QOSC_parasitics.wmf
Table 3-2
Typical values of parasitic capacitances
Name
Value
C20
4,6 pF
C21
FSK-: 2,8 pF / FSK+&ASK: 2.2pF
C22
1 pF
With the given parasitics the actual C_v can be calculated:
Cv- = Cv1 + Ctune1 + C21
[3 – 24]
Cv+ = -⁽--C-C---v--v--1-1---+--+---C-C---t--tu--u--n-n--e--e-1--1--⁾--+-^×---⁽-C--C--v--v--2-2---+--+---C--C---2-2--0-0---+--+---C--C--t--tu--u--n-n--e--e-2--2---⁾- + C21
[3 – 25]
Cvm
=
-⁽--C----v----1----+-----C----t--u----n---e---1----⁾---^×---⁽---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 – 26]
Note: Please keep in mind also to include the Pad parasitics of the circuit board.
Preliminary Specification
53
2003-02-18