CC2550_06 Datasheet, PDF (29/55 Pages) Texas Instruments – Single Chip Low Cost Low Power RF Transmitter

CC2550
Output power, typical,
+25^oC, 3.0 V [dBm]
(–55 or less)
–30
–28
–26
–24
–22
–20
–18
–16
–14
–12
–10
–8
–6
–4
–2
0
1
PATABLE
value
0x00
0x44
0x41
0x43
0x84
0x82
0x47
0xC8
0x85
0x59
0xC6
0x97
0xD6
0x7F
0xA9
0xBF
0xEE
0xFF
Current consumption,
typical [mA]
8.0
9.3
9.2
9.7
9.8
9.7
10.0
11.6
10.2
11.6
11.2
12.0
12.9
14.7
16.2
18.1
19.4
21.3
Table 20: Optimum PATABLE settings for various output power levels
22 Crystal Oscillator
A crystal in the frequency range 26-27 MHz
must be connected between the XOSC_Q1
and XOSC_Q2 pins. The oscillator is designed
for parallel mode operation of the crystal. In
addition, loading capacitors (C51 and C71) for
the crystal are required. The loading capacitor
values depend on the total load capacitance,
C_L, specified for the crystal. The total load
capacitance seen between the crystal
terminals should equal C_L for the crystal to
oscillate at the specified frequency.
C_L =
1
1
+
1
+ C _parasitic
C₅₁ C₇₁
The parasitic capacitance is constituted by pin
input capacitance and PCB stray capacitance.
Total parasitic capacitance is typically 2.5 pF.
The crystal oscillator circuit is shown in Figure
19. Typical component values for different
values of C_L are given in Table 21.
The crystal oscillator is amplitude regulated.
This means that a high current is used to start
up the oscillations. When the amplitude builds
up, the current is reduced to what is necessary
to maintain approximately 0.4 Vpp signal
swing. This ensures a fast start-up, and keeps
the drive level to a minimum. The ESR of the
crystal should be within the specification in
order to ensure a reliable start-up (see Section
4.3 on page 6).
XOSC_Q1
XOSC_Q2
XTAL
C51
C71
Figure 19: Crystal oscillator circuit
PRELIMINARY Data Sheet (Rev.1.2) SWRS039A
Page 29 of 54