MAS6179A2 datasheet(4/10 Pages) MAS

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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

Open

Power down

High

Low

Open

QO1

Frequency 1

Low

High

Closed

Open

QO2

Frequency 2, RFI2 capacitor

connected in parallel with antenna

Low

Closed

QO3

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.

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.

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

medium

frequency

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.

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.

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