CC2400 Datasheet, PDF (17/84 Pages) Texas Instruments – 2.4 GHz Low-Power RF Transceiver

CC2400
16 Application Circuit
Few external components are required for
the operation of CC2400. A typical
application circuit is shown in Figure 3. A
description of the external components
referring to Figure 3 are described in
Table 10. The bill of materials (BOM) is
given in Table 11.
Good PCB layout is vital for proper
operation, please see the section on PCB
Layout Recommendations on page 56 for
more details.
16.1 Input / output matching
The RF input/output is high impedance
and differential. The optimum differential
load for the RF port is listed on page 8.
When using an unbalanced antenna like a
monopole, a balun should be used in
order to get optimum performance. The
balun can be implemented using low-cost
discrete inductors and capacitors. The
balun consists of C61, C62, C71, C81,
L61, L62 and L72, and will match the RF
input/output to 50 Ω, see Figure 3. L61
and L62 also provide DC biasing of the
LNA/PA input/output. L71 is used to
isolate the TXRX_SWITCH pin. An
internal T/R switch circuit is used to switch
between the LNA and the PA. See
“Input/output matching” on page 50 for
more details.
If a balanced antenna, like a folded dipole,
is used, the balun can be omitted. If the
antenna also provides a DC path from the
TXRX_SWITCH pin to the RF pins,
inductors are not needed for DC biasing.
The L71 isolation inductor should still be
used to avoid antenna reflections. Figure 4
shows a typical application circuit with
differential antenna. The dipole has a
virtual ground point, hence bias is
provided without degradation in antenna
performance. Please note that a
differential antenna is generally larger than
an equivalent single-ended antenna.
16.2 Bias resistor
The bias resistor R451 is used to set an
accurate bias current for the chip.
16.3 Crystal
An external crystal with input and output
loading capacitors (C421 and C431) is
used for the crystal oscillator. See page 49
for details.
16.4 Digital I/O
The supply voltage for the digital I/O must
match the interfacing microcontroller. The
digital I/Os of CC2400 can interface
microcontrollers with supply voltages in
the range 1.6 – 3.6 V.
16.5 Power supply decoupling and
filtering
Proper power supply decoupling must be
used for optimum performance. The
placement and size of the decoupling
capacitors and the power supply filtering
are very important to achieve the best
performance in an application. Chipcon
provides a compact reference design that
should be followed very closely.
16.6 Power supply switching
As described in a note in the Absolute
Maximum Ratings section, the voltage
supply to the chip core should not be
switched off separately from the I/O supply
voltage.
If it is necessary to switch the core power
supply off, for instance to save the power
dissipated in the 1.8V regulator, the I/O
supply should be turned off as well. This
can be done quite easily by running the
I/O supply from a microcontroller I/O pin.
Current drawn on the I/O supply is just a
few milliamps, so an ordinary I/O pin
should have no problems in sourcing this
current. Power sequencing should be
performed so that both supplies are turned
on and off simultaneously.
SWRS042A
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