CC2430 Datasheet, PDF (29/234 Pages) Texas Instruments – A True System-on-Chip solution for 2.4 GHz IEEE 802.15.4 / ZigBee-TM

CC2430
11 Application Circuit
Few external components are required for the
operation of CC2430. A typical application
circuit is shown in Figure 6. Typical values and
description of external components are shown
in Table 24
11.1 Input / output matching
The RF input/output is high impedance and
differential. The optimum differential load for
the RF port is 115+j180 Ω.
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
LNA and the PA. See Input/output matching
section on page 184 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 6 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 189.
11.2 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.
11.3 Crystal
An external 32 MHz crystal, XTAL1, with two
loading capacitors (C191 and C211) is used
for the 32 MHz crystal oscillator. See page 16
for details.
XTAL2 is an optional 32.768 kHz crystal. Mesh
networks can be implemented without the
32.768 kHz crystal.
11.4 Voltage regulators
The on chip voltage regulators supply all 1.8 V
power supply pins and internal power supplies.
C241 and C421 are required for stability of the
regulators. A series resistor may be used to
comply with the ESR requirement.
11.5 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. Refer to the section PCB Layout
Recommendation on page 188.
CC2430 PRELIMINARY Data Sheet (rev. 1.03) SWRS036A
Page 29 of 232