CC2510FX Datasheet, PDF (190/253 Pages) List of Unclassifed Manufacturers – True System-on-Chip with Low Power RF Transceiver and 8051 MCU

CC2510Fx / CC2511Fx
14 Crystal Oscillator
14.1 CC2510Fx Crystal Oscillator
A crystal in the frequency range 26 MHz-
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 (C201 and C211) 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
C₂₁₁ C₂₀₁
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 7. Typical component values for
different values of C_L are given in Table 9.
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 Table 9 on page 15).
14.2 CC2511Fx Crystal Oscillator
The CC2511Fx requires a 48 MHz
frequency crystal to be used. If a
fundamental crystal is used, only the
loading capacitor values need to be
changed compared to the CC2510Fx
crystal oscillator. If a 3^rd overtone crystal is
used, an additional inductor and capacitor
is needed. Figure 9 shows this
configuration. Values for capacitors and
the inductor are given in Table 27.
CC2510Fx/CC2511Fx PRELIMINARY Data Sheet (Rev. 1.2) SWRS055A Page 190 of
252