DA9179.002
19 May, 2005
FREQUENCY SELECTION
The frequency selection and power down control is
accomplished via two digital control pins PDN1 and
PDN2. The control logic is presented in table 1.
Table 1
Frequency selection and power down control
PDN2
RFI2 Switch RFI3 Switch
PDN1
High
High
Low
Low
High
Low
High
Low
Open
Open
Closed
Closed
Open
Open
Open
Closed
Selected Crystal
Output
-
QO1
QO2
QO3
Description
Power down
Frequency 1
Frequency 2, RFI2 capacitor
connected in parallel with antenna
Frequency 3, RFI2 and RFI3
capacitors connected in parallel
with antenna
The internal antenna tuning capacitor switches
(RFI2, RFI3) and crystal filter output switches
(QO1, QO2, QO3) are controlled according table 1.
See switches in block diagram on page 1.
If frequency 1 is selected the RFI2 and RFI3
switches are open and only crystal output QO1 is
active. Antenna frequency is determined by
antenna inductor L
ANT
(see Typical Application on
page 5), antenna capacitor C
ANT1
and parasitic
capacitances related to antenna inputs RFIP, RFIM,
RFI2
and
RFI3
(see
Antenna
Tuning
Considerations below). Frequency 1 is the highest
frequency of the three selected frequencies.
If frequency 2 is selected then RFI2 switch is closed
to connect C
ANT2
to pin RFIM in parallel with ferrite
antenna and tune it to frequency 2. Then only
crystal output QO2 is active. Frequency 2 is the
medium frequency of the three selected
frequencies.
If frequency 3 is selected both RFI2 and RFI3
switches are closed to connect both C
ANT2
and
C
ANT3
capacitors to RFIM pin in parallel with ferrite
antenna and tune it to frequency 3. Then only
crystal QO3 is active. Frequency 3 is the lowest
frequency of the three selected frequencies.
It is recommended to switch the device to power
down for 50ms before switching to another
frequency. This guarantees fast startup in switching
to another frequency. The 50ms power down period
is used to discharge AGC capacitor and to initialize
fast startup conditions.
3 (9)
MAS [ MICRO ANALOG SYSTEMS ]
