CC2520_11 Datasheet, PDF (30/133 Pages) Texas Instruments – 2.4 GHZ IEEE 802.15.4/ZIGBEE RF TRANSCEIVER

CC2520 DATASHEET
2.4 GHZ IEEE 802.15.4/ZIGBEE® RF TRANSCEIVER
SWRS068 – DECEMBER 2007
C172
C173
SMA
connector
R201
C174
PCB
antenna
Figure 4: Actual board layout of the RF section of the reference design (rev 2.1).
9.2 Bias Resistor
The bias resistor R231 is used to set an accurate bias current. A high precision (±1%) 56kΩ resistor should
be used.
9.3 Crystal
An external 32MHz crystal with two loading capacitors (C121 and C131) is used for the crystal oscillator.
It is possible to feed a single-ended signal to the XOSC32M_Q1 pin and thus not use a crystal.
9.4 Digital Voltage Regulator
The on chip voltage regulator supplies 1.8 V to the digital part of CC2520. C271 is a decoupling capacitor for
the voltage regulator. Note that this should not be used to provide power to other IC’s.
9.5 Power Supply Decoupling and Filtering
Proper power supply decoupling must be used for optimum performance. This is shown as a lumped
capacitor C1 in Figure 4. The placement and size of the decoupling capacitors and the power supply filtering
are very important to achieve the best performance in an application. TI provides a compact reference
design that should be followed very closely.
9.6 Board Layout Guidelines
It is highly recommended to copy the board layout from the reference design [5].
• It is recommended to use star topology for the power supplies to CC2520.
• The power supply decoupling capacitor C1 is a lumped component. On the actual board layout
there should be separate decoupling capacitors as close to each of the power pins as possible.
• The balun is highly layout sensitive. The inductors in Figure 4 are actually transmission lines
embedded in the PCB and their values must be adapted according to the board layout. The values
of the capacitors C192, C172, C173 and C174 must also be adapted to the actual board layout.
• The GPIO pins can be configured to use internal pull-up resistors. They are not enabled after a
reset or in LPM2. Remember to take the default GPIO configuration into consideration when
connecting these signals, because there will be some time before the MCU is able to change the
configuration. In LPM2 GPIO5 (which is configured as an input) should be connected to either
30
WWW.TI.COM