TDA5252G2 Datasheet, PDF (43/86 Pages) Infineon Technologies AG – ASK/FSK 915MHz Wireless Transceiver

TDA5252 G2
Version 1.1
Application
E=
P
O
VI
SC
[3 – 10]
The diagram of Figure 3-7 has been measured directly at the PA-output at V_S=3V. A power loss in
the matching circuit of about 3dB will decrease the output power. As shown in the diagram, 250
Ohm is the optimum impedance for operation at 3V. For an approximation of R_OPT and P_OUT at
other supply voltages those 2 formulas can be used:
R_OPT ~ VS
and
[3 – 11]
P ~R
OUT
OPT
[3 – 12]
The behaviour of the power amplifier over the impedance and frequency is in principle the same as
of the TDA5250, but of course strongly depends on the matching network. (see also specification
of TDA5250)
Power_E_vs_RL.wmf
Figure 3-7 Output power P_o (mW) and collector efficiency E vs. load resistor R_L.
The DC collector current Ic of the power amplifier and the RF output power Po vary with the load
resistor RL. This is typical for overcritical operation of class C amplifiers. The collector current will
show a characteristic dip at the resonance frequency for this type of “overcritical” operation. The
depth of this dip will increase with higher values of RL.
Data Sheet
43
2007-02-26