CC2550 Datasheet, PDF (27/50 Pages) Texas Instruments – Single Chip Low Cost Low Power RF-Transmitter

CC2550
26 VCO
The VCO is completely integrated on-chip.
26.1 VCO and PLL Self-Calibration
The VCO characteristics will vary with
temperature and supply voltage changes, as
well as the desired operating frequency. In
order to ensure reliable operation, CC2550
includes frequency synthesizer self-calibration
circuitry. This calibration should be done
regularly, and must be performed after turning
on power and before using a new frequency
(or channel). The number of XOSC cycles for
completing the PLL calibration is given in
Table 18 on page 25.
27 Voltage Regulators
CC2550 contains several on-chip linear voltage
regulators, which generate the supply voltage
needed by 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 in Table 1 and Table 11
are not exceeded. The voltage regulator for
the digital core requires one external
decoupling capacitor.
Setting the CSn pin low turns on the voltage
regulator to the digital core and starts the
28 Output Power Programming
The RF output power level from the device has
two levels of programmability, as illustrated in
Figure 14. Firstly, the special PATABLE
register can hold up to eight user selected
output power settings. Secondly, the 3-bit
FREND0.PA_POWER value selects the
PATABLE entry to use. This two-level
functionality provides flexible PA power ramp
up and ramp down at the start and end of
transmission. All the PA power settings in the
PATABLE from index 0 up to the
FREND0.PA_POWER value are used.
The calibration can be initiated automatically
or manually. The synthesizer can be
automatically calibrated each time the
synthesizer is turned on, or each time the
synthesizer is turned off. This is configured
with the MCSM0.FS_AUTOCAL register setting.
In manual mode, the calibration is initiated
when the SCAL command strobe is activated
in the IDLE mode. The default setting is to
calibrate each time the frequency synthesizer
is turned on.
The calibration values are not maintained in
sleep mode. Therefore, the CC2550 must be
recalibrated after reprogramming the
configuration registers when the chip has been
in the SLEEP state.
crystal oscillator. The SO pin on the SPI
interface must go low before using the serial
interface (setup time is TBD).
On initial power up, the MCU must set CSn low
and issue the reset command strobe SRES.
If the chip is programmed to enter power-down
mode, (SPWD 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 output should only be
used for driving the CC2550.
Preliminary Data Sheet (rev. 1.1) SWRS039
Page 27 of 51