CC2550_06 Datasheet, PDF (10/55 Pages) Texas Instruments – Single Chip Low Cost Low Power RF Transmitter

CC2550
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 a
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.
7 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 LC 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. It is 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
C41
C51/C71
C101/C111
C102/C112
C103/C104
L101/L111
L102
R141
XTAL
Description
100 nF decoupling capacitor for on-chip voltage regulator to digital part
Crystal loading capacitors, see Section 22 on page 29 for details
RF balun DC blocking capacitors
RF balun/matching capacitors
RF LC filter/matching capacitors
RF balun/matching inductors (inexpensive multi-layer type)
RF LC filter inductor (inexpensive multi-layer type)
Resistor for internal bias current reference
26-27 MHz crystal, see Section 22 on page 29 for details
Table 12: Overview of external components (excluding supply decoupling capacitors)
PRELIMINARY Data Sheet (Rev.1.2) SWRS039A
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