TDA5252G2 Datasheet, PDF (49/86 Pages) Infineon Technologies AG – ASK/FSK 915MHz Wireless Transceiver

TDA5252 G2
Version 1.1
Application
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 _±
CL
+−
C0
⋅
N---^∆---⋅^-f--f-
⋅

1

+
2-----⋅_---(_{--C----C-0---1-+-----C----L----})_{-}
= -----------------------------------------------------------------------------------------
1
±
N---^∆---⋅^-f--f-
⋅

1

+
-2----^â‹---⁽--C----C-0---1-+-----C----L----⁾-_{}
[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
∆f:
peak frequency deviation
With C_L+ and C_L- the necessary C_v+ for FSK HIGH and C_v- for FSK LOW can be calculated.
Alternatively, an external AC coupled (10nF in series to 1kΩ) signal can be applied at pin 19 (Xout).
The drive level should be approximately 100mVpp.
3.2.1 Synthesizer Frequency setting
Generating ASK and FSK modulation 3 setable frequencies are necessary.
3.2.1.1 Possible crystal oscillator frequencies
The resulting possible crystal oscillator frequencies are shown in the following Figure 3-13
RX:
FSK
TX: FSK-
ASK
ASK
FSK+
Deviation Deviation
f₁
f₀
f₂
Nominal
Frequency
free_reg.wmf
Figure 3-13 possible crystal oscillator frequencies
In ASK receive mode the crystal oscillator is set to frequency f₂ to realize the necessary frequency
offset to receive the ASK signal at f₀*N (N: division ratio of the PLL).
Data Sheet
49
2007-02-26