TDA5250D2 Datasheet, PDF (45/97 Pages) Infineon Technologies AG – ASK/FSK 868MHz Wireless Transceiver

confidential
TDA 5250 D2
preliminary
Applications
4.1.1.2 Switch in TX-Mode
The evalboard can be set into the TX-Mode by grounding the RX/TX-jumper on
the evalboard or programming the TDA5250 to operate in the TX-Mode. If the
IC is programmed to operate in the TX-Mode, the RX/TX-pin will act as an open
drain output at a logical LOW. Then a DC-current can flow from VCC to GND
via L1, L2, D1, R1 and D2.
The current
I _{PIN −DIODE}
is:
=
Vcc
−
2
∗ V_{FORWARD ,PIN −DIODE}
R₁
[4 – 7]
Now both pin-diodes are biased with a current of approx. 0.3mA@3V and have
a very low impedance for RF.
RF I/O
C1
50 Ohm
SM A-connector
C2
grounded RX/TX
(with jum per or
RX/TX-pin of IC)
VCC
C5
L1
L2
PA
C3
C4
R1
C7
C9
L3 ^C10
C6
LNI
LN IX
R X/T X
Figure 4-4 TX_Mode
TX_Mode.wmf
R1 does not influence the matching because of its very high resistance. Due to
the large capacitance of C1, C6 and C5 the circuit can be further simplified for
RF:
RF I/O
50 Ohm
C2
S M A-connector
L1
L2
PA
C3
C4
C7
C9
LNI
LNIX
L3 ^C10
Figure 4-5 TX_Mode_simplified
TX_Mode_simplified.wmf
Wireless Components
4-5
Specification, July 2002