DA6179.000
22 January, 2007
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
PDN1
PDN2
RFI2 Switch RFI3 Switch Selected Crystal
Output
Description
High
High
Open
Open
-
Power down
Frequency 1
Frequency 2, RFI2 capacitor
connected in parallel with antenna
Frequency 3, RFI2 and RFI3
capacitors connected in parallel
with antenna
High
Low
Low
High
Open
Closed
Open
Open
QO1
QO2
Low
Low
Closed
Closed
QO3
The internal antenna tuning capacitor switches
(RFI2, RFI3) and crystal filter output switches (QO1,
QO2, QO3) are controlled according table 1.
medium frequency of the three selected
frequencies.
If frequency 3 is selected both RFI2 and RFI3
switches are closed to connect both CANT2 and CANT3
capacitors to RFIM pin in parallel with ferrite
antenna and tune it to frequency 3. Then only
crystal output QO3 is active. Frequency 3 is the
lowest frequency of the three selected frequencies.
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 LANT (see Typical Application on page 6),
antenna capacitor CANT1 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.
It is recommended to switch the device to power
down for at least 50ms before switching to another
frequency. This guarantees fast startup in switching
to another frequency. During minimum 50ms power
down time the AGC capacitor voltage is completely
pulled to VDD and the proper fast startup conditions
are met. Without proper fast startup control the
startup time can be several minutes. With fast
startup it is shortened typically to few seconds.
If frequency 2 is selected then RFI2 switch is closed
to connect CANT2 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
4 (10)
MAS [ MICRO ANALOG SYSTEMS ]
