CC2480_11 Datasheet, PDF (20/48 Pages) Texas Instruments – Z-Accel 2.4 GHz ZigBee Processor

CC2480
8 Application Circuit
Few external components are required for the
operation of CC2480. A typical application
circuit is shown in Figure 5. Typical values and
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 a 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.}
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:
C_L =
1
1
+
1
+ C _parasitic
C₁₉₁ C₂₁₁
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
8.4 Voltage regulators
The on chip voltage regulators supply all 1.8 V
power supply pins and internal power supplies.
description of external components are shown
in Table 19.
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 to the section Antenna
Considerations on page 35.
sleep current consumption and accurate wake
up times. The load capacitance seen by the
32.768 kHz crystal is given by:
C_L =
1
1
+
1
+ C _parasitic
C₄₄₁ C₄₃₁
A series resistor may be used to comply with
the ESR requirement.
C241 and C421 are required for stability of the
regulators.
CC2480 Data Sheet SWRS074A
Page 20 of 43