CC1110Fx / CC1111Fx
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
10.4 USB (
CC1111Fx
)
For the
CC1111Fx
, the DP and DM pins need
series resistors R262 and R263 for impedance
matching and the D+ line must have a pull-up
resistor, R264. The series resistors should
match the 90
Ω
±15% characteristic
impedance of the USB bus.
Notice that the pull-up resistor must be tied to
a voltage source between 3.0 and 3.6 V
(typically 3.3 V). The voltage source must be
derived from or controlled by the V
BUS
power
supply provided by the USB cable. In this way,
10.5 Power Supply Decoupling
The power supply must be properly decoupled
close to the supply pins. Note that decoupling
capacitors are not shown in the application
circuit. The placement and the size of the
decoupling capacitors are very important to
achieve the optimum performance. TI provides
reference designs that should be followed
closely ([1], [2], [3] and [4]).
the pull-up resistor does not provide current to
the D+ line when V
BUS
is removed. The pull-up
resistor may be connected directly between
V
BUS
and the D+ line. As an alternative, if the
CC1111Fx
firmware needs the ability to
disconnect from the USB bus, an I/O pin on
the
CC1111Fx
can be used to control the pull-up
resistor.
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
18 XOSC32_Q2
AVDD_DREG 29
17 XOSC32_Q1
GUARD 28
20 XOSC_Q2
RBIAS 27
Figure 10: Application Circuit for
CC1110Fx
315/433 MHz (excluding supply decoupling capacitors)
21 XOSC_Q1
19 AVDD
SWRS033E
Page 37 of 239
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