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
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
10.4 USB (CC1111Fx)
the pull-up resistor does not provide current to
the D+ line when VBUS is removed. The pull-up
resistor may be connected directly between
VBUS 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.
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 VBUS 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]).
Figure 10: Application Circuit for CC1110Fx 315/433 MHz (excluding supply decoupling capacitors)
SWRS033E
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