CC2520_11 Datasheet, PDF (31/133 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
ground or VDD. The other GPIO pins should be grounded or high impedance. Failing to do this, will
result in significantly higher current consumption than necessary.
• The SO pin is configured as an input when CSn is high or the device is in reset or LPM2. This
makes it possible to connect multiple SPI slaves to one SPI master. This pin should not be left
floating when in LPM2, as this will draw more current than necessary. If the voltage level can not be
controlled in any other way, use a 1MOhm pull-down resistor.
• The crystal input lines should be routed as far away from each other as practically possible.
• The NC pins can be left floating.
• Glitches on the digital inputs may create serious issues in a system design. The digital input pads
have Schmitt-triggers to help make them less sensitive to glitches, but the board layout should still
avoid routing the digital input lines close to other noisy signals.
9.7 Antenna Considerations
The reference design contains two antenna options. As default, the SMA connector is connected to the
balun through a 0Ω resistor. This resistor can be soldered off and rotated 90° clockwise in order to connect
to the PCB antenna, which is a planar inverted F antenna (PIFA).
Note that all testing and characterization has been done using the SMA connector. The PCB antenna has
only been functionally tested by establishing a link between two EMs. In our experiment, the PCB antenna
gave approximately the same range as when using an antenna connected to the SMA connector.
Please refer to the antenna selection guide [12] and the Inverted F antenna app note [11] for further details.
9.8 Choosing the Most Suitable Interconnection with a Microcontroller
• Connect the 4 SPI signals; CSn, SCLK, SI and SO to the microcontroller.
These signals are required in order to configure CC2520 and exchange data with it.
• Connect RESETn to the microcontroller. Using the RESETn signal is the recommended way to
reset CC2520 for instance after powering up. If saving a pin is critical, the RESETn pin can be
connected to VDD. The CC2520 can still be reset with the SRES command strobe. This will also
require a manual start of the crystal oscillator by issuing a SXOSCON command strobe.
• Connecting VREG_EN to the microcontroller will make it possible to put CC2520 into LPM2 to save
power. VREG_EN may be connected to VDD and thus always leave the regulator on. If power
saving is not important in the target application, this may be an acceptable way of saving a pin.
• Connecting one or more of the GPIOs to the microcontroller is optional.
The number of GPIOs to connect depends on the application. Connecting more GPIOs to the
microcontroller generally gives more flexibility and less SPI traffic because it reduces the need to
keep reconfiguring the GPIOs for different uses.
• If CC2520 will be providing clock to the microcontroller, GPIO0 should be connected to the clock
input of the microcontroller. After reset, GPIO0 will output a 1MHz clock signal with 50/50 duty cycle.
The digital IO of CC2520 is described in more detail from section 12.
9.9 Interfacing CC2520 and MSP430F2618
The MSP430F2618 is well suited for use with the CC2520. The suggested interfacing of these two chips is
given in Table 5. The interconnections shown in Table 6 are exactly the same as is used in the CC2520
development kit [5].
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