TDA7110 Datasheet, PDF (27/39 Pages) Infineon Technologies AG – ASK/FSK Transmitter 868/433 MHz

TDA7110
Applications
If the FSK switch is closed, Cv_ is equal to Cv1 (C6 in the application diagram).
If the FSK switch is open, Cv2 (C7 in the application diagram) can be calculated.
Cv2 = C7 = ^{Csw ∗Cv1− (Cv+) ∗(Cv1+ Csw)}
(Cv+) − Cv1
Csw:
parallel capacitance of the FSK switch (3 pF incl. layout parasitics)
Remark: These calculations are only approximations. The necessary values
depend on the layout also and must be adapted for the specific
application board.
The 434 MHz 50Ω-Output testboard shows an FSK-deviation of +/- 24 kHz, typically.
The 868 MHz 50Ω-Output testboard shows an FSK-deviation of +/- 27 kHz, typically.
3.5 Design hints on the buffered clock output (CLKOUT)
The CLKOUT pin is an open collector output. An external pull up resistor (RL)
should be connected between this pin and the positive supply voltage. The
value of RL is depending on the clock frequency and the load capacitance CLD
(PCB board plus input capacitance of the microcontroller). RL can be calculated
to:
RL =
1
fCLKOUT *8*CLD
Table 3-2
CL[pF]
5
10
20
fCLKOUT=
847 kHz
RL[kΩ]
27
12
6.8
fCLKOUT=
3.39 MHz
CL[pF]
RL[kΩ]
5
6.8
10
3.3
20
1.8
Remark: To achieve a low current consumption and a low
spurious radiation, the largest possible RL should be chosen.
Wireless Components
3-7
Data Sheet, December 2008