TDA5250D2 Datasheet, PDF (60/97 Pages) Infineon Technologies AG – ASK/FSK 868MHz Wireless Transceiver

confidential
TDA 5250 D2
preliminary
Applications
Table 4-2 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:
C_v- = C_v1 + C_tune1 + C₂₁
C_v+
=
(_---C_{----v---1----}+_-----C_{----t-u---n---e--1---})_----⋅_---(_--C_{----v---2----}+_-----C_----2--0----+_-----C_{----t--u---n--e---2---})
C_v1 + C_tune1 + C_v2 + C₂₀ + C_tune2
+
C₂₁
[4 – 24]
[4 – 25]
C_vm
=
(_---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---})
C_v1 + C_tune1 + C_v2 + C₂₀ + C_v3 + C₂₂ + C_tune2
+
C₂₁
[4 – 26]
Note: Please keep in mind also to include the Pad parasitics of the circuit board.
4.2.4 Calculation of the external capacitors
1. Determination of necessary crystal frequency using formula [4-19].
e.g. f_FSK- = f_{COSC LOW}
2. Determine corresponding C_Load applying formula [4-18].
e.g. C_{L FSK}- = C_{L ±}
3. Necessary C_V using formula [4-17].
e.g.
( ) ^{CV − =}
1
C_{L,FSK −}
+
1
2πf_{FSK −}
2 _{* LOSC}
4. When the necessary C_v for the 3 frequencies (C_v- for FSK LOW, C_v+ for FSK
HIGH and C_vm for FSK-receive) are known the external capacitors and the
internal tuning caps can be calculated using the following formulas:
-FSK:
+FSK:
FSK_RX:
C_v1 + C_tune1 = C_v- – C₂₁
C_v2 + C_tune2
=
(_---C_{----v---1----}+_-----C_{----t-u---n---e--1---})_----⋅_---(_--C_{----v---+----}–_-----C_----2---1---)
(C_v1 + C_tune1)–(C_v+ – C₂₁)
–
C₂₀
C_v3 + C_tune2
=
-⁽---^C----^v---¹----⁺----^C-----^t-^u---ⁿ---^e--¹---⁾---^â‹---⁽---^C----^v---^m-----^–----^C-----²--¹---⁾-
(C_v1 + C_tune1) – (C_vm – C₂₁)
–
C₂₀
–
C_v2
–
C₂₂
[4 – 27]
[4 – 28]
[4 – 29]
Wireless Components
4 - 20
Specification, July 2002