CC2550-RTR1 datasheet(10/55 Pages) TI

10 / 55 page

CC2550

PRELIMINARY Data Sheet (Rev.1.2)

SWRS039A

Page 10 of 54

A simplified block diagram of

CC2550 is shown

in Figure 2.

The

CC2550 transmitter is based on direct

synthesis of the RF frequency.

The

frequency

synthesizer

includes

completely on-chip LC VCO.

A crystal is to be connected to XOSC_Q1 and

XOSC_Q2. The crystal oscillator generates the

reference frequency for the synthesizer, as

well as clocks for the digital part.

A 4-wire SPI serial interface is used for

configuration and data buffer access.

The digital baseband includes support for

channel configuration, packet handling and

data buffering.

Application Circuit

Only a few external components are required

for using the

CC2550. The recommended

application circuit is shown in Figure 3. The

external components are described in Table

12, and typical values are given in Table 13.

Bias resistor

The bias resistor R141 is used to set an

accurate bias current.

Balun and RF matching

C102, C112, L101 and L111 form a balun that

converts the differential RF signal on

CC2550

to a single-ended RF signal. C101 and C111

are needed for DC blocking. Together with an

appropriate

network,

the

balun

components also transform the impedance to

match a 50

Ω antenna (or cable). Component

values for the RF balun and LC network are

easily found using the SmartRF® Studio

software. Suggested values are listed in Table

13. The balun and LC filter component values

and their placement are important to keep the

performance

optimized.

highly

recommended to follow the CC2550EM

reference design.

Crystal

The crystal oscillator uses an external crystal

with two loading capacitors (C51 and C71).

See Section 22 on page 29 for details.

Power supply decoupling

The power supply must be properly decoupled

close to the supply pins. Note that decoupling

capacitors are not shown in the application

circuit. The placement and the size of the

decoupling capacitors are very important to

achieve

the optimum performance.

The

CC2550EM reference design should be

followed closely.

Component

Description

C41

100 nF decoupling capacitor for on-chip voltage regulator to digital part

C51/C71

Crystal loading capacitors, see Section 22 on page 29 for details

C101/C111

RF balun DC blocking capacitors

C102/C112

RF balun/matching capacitors

C103/C104

RF LC filter/matching capacitors

L101/L111

RF balun/matching inductors (inexpensive multi-layer type)

L102

RF LC filter inductor (inexpensive multi-layer type)

R141

Resistor for internal bias current reference

XTAL

26-27 MHz crystal, see Section 22 on page 29 for details

Table 12: Overview of external components (excluding supply decoupling capacitors)

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