Texas Instruments 3138 155 232931 - Manual (Page 51)

CC2420
SWRS041B Page 51 of 89
27 VCO and PLL Self-Calibration
27.1 VCO
The VCO is completely integrated and
operates at 4800 – 4966 MHz. The VCO
frequency is divided by 2 to generate
frequencies in the desired band (2400-
2483.5 MHz).
27.2 PLL self-calibration
The VCO's characteristics will vary with
temperature, changes in supply voltages,
and the desired operating frequency.
In order to ensure reliable operation the
VCO’s bias current and tuning range are
automatically calibrated every time the RX
mode or TX mode is enabled, i.e. in the
RX_CALIBRATE, TX_CALIBRATE and
TX_ACK_CALIBRATE control states in
Figure 25 on page 44.
28 Output Power Programming
The RF output power of the device is
programmable and is controlled by the
TXCTRL.PA_LEVEL
register. Table 9
shows the output power for different
settings, including the complete
programming of the TXCTRL control
register. The typical current consumption
is also shown.
PA_LEVEL TXCTRL register Output Power [dBm] Current Consumption [mA]
31 0xA0FF 0 17.4
27 0xA0FB -1 16.5
23 0xA0F7 -3 15.2
19 0xA0F3 -5 13.9
15 0xA0EF -7 12.5
11 0xA0EB -10 11.2
7 0xA0E7 -15 9.9
3 0xA0E3 -25 8.5
Table 9. Output power settings and typical current consumption @ 2.45 GHz
29 Voltage Regulator
CC2420 includes a low drop-out voltage
regulator. This is used to provide a 1.8 V
power supply to the
CC2420 power
supplies. The voltage regulator should not
be used to provide power to other circuits
because of limited power sourcing
capability and noise considerations.
The voltage regulator input pin VREG_IN
is connected to the unregulated 2.1 to 3.6
V power supply. The voltage regulator is
enabled / disabled using the active high
voltage regulator enable pin VREG_EN.
The regulated 1.8 V voltage output is
available on the VREG_OUT pin. A
simplified schematic of the voltage
regulator is shown in Figure 28.
The voltage regulator requires external
components as described in the
Application Circuit section on page 19.
When disabling the voltage regulator, note
that register and RAM programming will
be lost as leakage current reduces the
output voltage on the VREG_OUT pin below
1.6 V.
CC2420 should then be reset before
the voltage regulator is disabled.