CC2480 datasheet(20/48 Pages) TI

20 / 48 page

CC2480

Application Circuit

Few external components are required for the

operation of

CC2480. A typical application

circuit is shown in Figure 5. Typical values and

description of external components are shown

in Table 19.

8.1

Input / output matching

The RF input/output is high impedance and

differential. The optimum differential load for

the RF port is 60 + j164

Ω4.

When using an unbalanced antenna such as a

monopole, a balun should be used in order to

optimize performance. The balun can be

implemented using low-cost discrete inductors

and capacitors. The recommended balun

shown, consists of C341, L341, L321 and

L331

together

with

PCB

microstrip

transmission line (λ/2-dipole), and will match

the RF input/output to 50

Ω. An internal T/R

switch circuit is used to switch between the

4 This is for 2440MHz.

LNA (RX) and the PA (TX). See Input/output

matching section on page 33 for more details.

If a balanced antenna such as a folded dipole

is used, the balun can be omitted. If the

antenna also provides a DC path from

TXRX_SWITCH

pin to the RF pins, inductors

are not needed for DC bias.

Figure 5 shows a suggested application circuit

using a differential antenna. The antenna type

is a standard folded dipole. The dipole has a

virtual ground point; hence bias is provided

without degradation in antenna performance.

Also

refer

the

section

Antenna

Considerations on page 35.

8.2

Bias resistors

The bias resistors are R221 and R261. The

bias resistor R221 is used to set an accurate

bias current for the 32 MHz crystal oscillator.

8.3

Crystal

An external 32 MHz crystal, XTAL1, with two

loading capacitors (C191 and C211) is used

for the 32 MHz crystal oscillator. See page 10

for details. The load capacitance seen by the

32 MHz crystal is given by:

parasitic

211

191

XTAL2 is an optional 32.768 kHz crystal, with

two loading capacitors (C441 and C431), used

for the 32.768 kHz crystal oscillator. The

32.768 kHz crystal oscillator is used in

applications where you need both very low

sleep current consumption and accurate wake

up times. The load capacitance seen by the

32.768 kHz crystal is given by:

parasitic

431

441

A series resistor may be used to comply with

the ESR requirement.

8.4

Voltage regulators

The on chip voltage regulators supply all 1.8 V

power supply pins and internal power supplies.

C241 and C421 are required for stability of the

regulators.

CC2480 Data Sheet SWRS074A

Page 20 of 43

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