CC400-RTR2 datasheet(20/31 Pages) TI

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CC400

SWRS050

Page 20 of 32

26.

System Considerations and Guidelines

26.1.

Low-cost systems

In systems where low cost is of great

importance the 200 kHz IF should be

used. The oscillator crystal can then be a

low cost crystal with 50 ppm frequency

tolerance.

26.2.

Battery operated systems

In low power applications the power down

mode should be used when not being

active. Depending on the start-up time

requirement, the oscillator core can be

powered during power down. Precharging

of the demodulator may also be used to

reduce the receiver turn-on time, see

description p.21.

26.3.

Narrow band systems

CC400 is also suitable for use in narrow

band systems. However, it is then required

to use a crystal with low temperature drift

and ageing. A trimmer capacitor in the

crystal oscillator circuit (in parallel with

C151) may also be necessary to set the

initial frequency.

It is also possible to include an external IF-

filter at 455 kHz. This should be a ceramic

filter with 1.5 k

Ω input/output impedance

connected between IF_OUT and IF_IN.

Typical bandwidth is 30 kHz. Due to the

high Q of such a filter, a better selectivity

can be achieved. See Application Note

AN005 “Selecting system parameters and

system configurations using CC400 /

CC900” for more details.

26.4.

High reliability systems

Using a SAW filter as a preselector will

improve the communication reliability in

harsh environments by reducing the

probability of blocking.

26.5.

Spread spectrum frequency

hopping systems

Due to the very fast frequency shift

properties of the PLL, the

CC400 may very

well be used in frequency hopping

systems.

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