CC112X/CC1175
SWRU295C
Page 67 of 108
9
System Considerations and Guidelines
9.1
Voltage Regulators
CC112X
contains several on-chip linear voltage regulators that generate the supply voltages needed by
the low-voltage modules. These voltage regulators are invisible to the user, and can be viewed as
integral parts of the various modules. The user must however make sure that the absolute maximum
ratings and required pin voltages are not exceeded.
By setting the CSn pin low, the voltage regulator to the digital core turns on and the crystal oscillator
starts. The SO pin on the SPI interface must go low before the first positive edge of SCLK (setup time
is given in Table 1.If the chip is programmed to enter power-down mode (
strobe
issued), the power will be turned off after CSn goes high. The power and crystal oscillator will be
turned on again when CSn goes low.
The voltage regulator for the digital core requires one external decoupling capacitor.
The voltage regulator output should only be used for driving the
CC112X
.
9.2
SRD Regulations
International regulations and national laws regulate the use of radio receivers and transmitters. Short
Range Devices (SRDs) for license free operation below 1 GHz are usually operated in the 169 MHz,
433 MHz, 868 MHz, 915 MHz, or 950 MHz frequency bands. The
CC112X
is specifically designed for
operation in these bands.
Please note that compliance with regulations is dependent on the complete system performance. It is
the customer‟s responsibility to ensure that the system complies with regulations.
9.3
Frequency Hopping and Multi-Channel Systems
The 433 MHz, 868 MHz, or 915 MHz bands are shared by many systems both in industrial, office, and
home environments. It is therefore recommended to use frequency hopping spread spectrum (FHSS)
or a multi-channel protocol because frequency diversity makes the system more robust with respect
to interference from other systems operating in the same frequency band. FHSS also combats
multipath fading.
CC112X
is highly suited for FHSS or multi-channel systems due to its agile frequency synthesizer and
effective communication interface. Using the packet handling support and data buffering is also
beneficial in such systems as these features will significantly offload the host controller.
Charge pump current, VCO current, and VCO capacitance array calibration data is required for each
frequency when implementing frequency hopping for
CC112X
. There are 2 ways of obtaining the
calibration data from the chip:
1) Frequency hopping with calibration for each hop.
2)
Fast frequency hopping without calibration for each hop can be done by performing the necessary
calibration at start-up and saving the resulting
, and
register values in
MCU memory
. Between each frequency hop, the calibration process can then be replaced by writing
the calibration values that corresponds to the next RF frequency.
The recommended settings change with frequency. This means that one should always use
SmartRF Studio to get the correct settings for a specific frequency before doing a calibration,
regardless of which calibration method is being used.
9.4
Continuous Transmissions
In data streaming applications, the
CC112X
opens up for continuous transmissions at an effective data
rate of up to 100 ksps (200 kbps). As the modulation is done with a closed loop PLL, there is no
limitation in the length of a transmission (open loop modulation used in some transceivers often
prevents this kind of continuous data streaming and reduces the effective data rate).
9.5
Battery Operated Systems
In low power applications, the SLEEP state with the crystal oscillator core switched off should be used
when the
CC112X
is not active. It is possible to leave the crystal oscillator core running in the SLEEP
state if start-up time is critical. The eWOR functionality should be used in low power applications.