CC1110FX_09 Datasheet, PDF(37/247 Page) Texas Instruments – Low-Power SoC (System-on-Chip) with MCU, Memory,Sub-1 GHz RF Transceiver, and USB Controller

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CC1110FX_09 Datasheet, PDF (37/247 Pages) Texas Instruments – Low-Power SoC (System-on-Chip) with MCU, Memory,Sub-1 GHz RF Transceiver, and USB Controller

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Total parasitic capacitance is typically 2.5 pF.

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

9.4 Reference Signal

The chip can alternatively be operated with a

reference signal from 26 to 27 MHz (CC1110Fx)

or 48 MHz (CC1111Fx) instead of a crystal. This

input clock can either be a full-swing digital

signal (0 V to VDD) or a sine wave of

maximum 1 V peak-peak amplitude. The

reference signal must be connected to the

XOSC_Q1 input. The sine wave must be

9.5 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 Î© Â±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,

9.6 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

CC1110Fx / CC1111Fx

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

connected to XOSC_Q1 using a serial

capacitor. When using a full-swing digital

signal this capacitor can be omitted. The

XOSC_Q2 line must be left un-connected. The

crystal loading capacitors and crystal inductor

(if using X4) can be omitted when using a

reference signal

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.

decoupling capacitors are very important to

achieve the optimum performance. TI provides

reference designs that should be followed

closely ([1], [2], [3] and [4]).

SWRS033G

Page 37 of 244

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