CC2510FX Datasheet, PDF (31/253 Pages) List of Unclassifed Manufacturers – True System-on-Chip with Low Power RF Transceiver and 8051 MCU

CC2510Fx / CC2511Fx
11 Application Circuit
This section describes the recommended
application circuit for the RF part of the
CC2510Fx/CC2511Fx, together with crystal
oscillator connections and USB.
Only a few external components are required
for using the CC2510Fx/CC2511Fx RF
transceiver. The recommended application
circuit for CC2510Fx is shown in Figure 7. The
recommended application circuits for CC2511Fx
are shown in Figure 8 and Figure 9. The first
circuit uses a fundamental crystal and the
second uses a 3^rd overtone crystal. The
external components are described in Table
26, and typical values are given in Table 27.
Notice that all application circuits are shown
excluding supply decoupling capacitors and
digital I/O.
11.1 Bias resistor
The bias resistor R271 is used to set an
accurate bias current. It is very important to
use the specified tolerance for this resistor.
11.2 Balun and RF matching
C232, C242, L231 and L241 form the
recommended balun that converts the
differential RF port on CC2510Fx/CC2511Fx to a
single-ended RF signal. (C241 and C231 are
also 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
27. The balun and LC filter component values
and their placement are important to keep the
performance optimized. It is recommended to
follow the CC2510EM / CC2511Dongle
reference design.
11.3 Crystal
The crystal oscillator for the CC2510Fx uses an
external crystal X1, with two loading capacitors
(C201 and C211). See section 14 on page 190
for details.
The CC2511Fx should use a 48 MHz
fundamental (X3) or a 48 MHz 3^rd overtone low
cost external crystal (X4). Depending on the
option selected, different loading capacitors
(C203, C214) or (C202, C212, C213) must be
used. When X4 is used, an inductor, L281,
must also be connected in series with C212.
The circuit also shows the connections for the
optional 32.768 kHz crystal oscillator, with
external crystal X2 and loading capacitors
C181 and C171. This crystal oscillator is used
by the Sleep Timer providing a real-time clock
function and is not required for radio operation.
The sleep timer may use the internal RC
oscillator as an alternative to X2. The internal
RC oscillator is less accurate but saves cost
and board space. When not using X2 P2_3
and P2_4 may be used as general IO pins.
11.4 USB (CC2511Fx)
For the CC2511Fx the DP and DM pins need
series resistors R262 and R263 for impedance
matching and the DP line must have a pull-up
resistor, R264. The series resistors should
match the 90Ω +/- 5% characteristic
impedance of the USB bus.
Notice that the pull-up resistor must be tied to
a voltage source between 3.0 and 3.6 V
(typically 3.3V). The voltage source must be
derived from or controlled by the V_BUS power
supply, provided by the USB cable, such that
when V_BUS is removed, the pull-up resistor
does not provide current to the D+ line. The
pull-up resistor may be connected direcly
between V_BUS and the D+ line. Or if the
CC2511Fx firmware need the ability to
disconnect from the USB bus,, a I/O pin on the
CC2511Fx can be used to control the pull-up
resistor.
11.5 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. Chipcon
provides a reference design that should be
followed closely.
CC2510Fx/CC2511Fx PRELIMINARY Data Sheet (Rev. 1.2) SWRS055A Page 31 of 252