CC2420 Chipcon AS, CC2420 Datasheet - Page 51

• Manufacturer Part Number: CC2420
• Description: 2.4 GHz RF Transceiver for IEEE 802.15.4 and ZigBee
• Manufacturer: Chipcon AS

Crystal Oscillator
An external clock signal or the internal
crystal oscillator can be used as main
frequency
frequency must be 16 MHz. Because the
crystal frequency is used as reference for
the data rate as well as other internal
signal
frequencies cannot be used.
If an external clock signal is used this
should be connected to XOSC16_Q1, while
XOSC16_Q2 should be left open. The
MAIN.XOSC16M_BYPASS bit must be set
when an external clock signal is used.
Using the internal crystal oscillator, the
crystal must be connected between the
XOSC16_Q1 and XOSC16_Q2 pins. The
oscillator is designed for parallel mode
operation of the crystal. In addition,
loading capacitors (C
crystal are required. The loading capacitor
values
capacitance, C
The total load capacitance seen between
the crystal terminals should equal C
the crystal to oscillate at the specified
frequency.
Chipcon AS SmartRF ® CC2420 Preliminary Datasheet (rev 1.0), 2003-11-17
depend
processing
Item
C6
C7
reference.
XOSC16_Q1
XOSC16_Q1
L
, specified for the crystal.
on
381
Table 10. Crystal oscillator component values
functions,
the
and C
C
6.8 pF
6.8 pF
The
L
= 12 pF
Figure 28. Crystal oscillator circuit
C391
C391
total
391
reference
) for the
other
L
load
for
XTAL
XTAL
XTAL
C
18 pF
18 pF
L
= 16 pF
SmartRF
The parasitic capacitance is constituted by
pin input capacitance and PCB stray
capacitance.
capacitance is typically 5 pF. A trimming
capacitor may be placed across C
initial tuning if necessary.
The crystal oscillator circuit is shown in
Figure 28. Typical component values for
different values of C
10.
The
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
a stable oscillation. This ensures a fast
start-up and keeps the drive level to a
minimum. The ESR of the crystal must be
within the specification in order to ensure
a reliable start-up (see the Electrical
Specifications section).
C
L
=
C
crystal
1
381
C381
C381
+
1
C
C
27 pF
27 pF
1
L
391
= 22 pF
oscillator
The
XOSC16_Q2
XOSC16_Q2
®
+
C
L
parasitic
are given in Table
CC2420
total
is
Page 51 of 85
amplitude
parasitic
381
for