CC2400-RTR1 datasheet(17/84 Pages) TI1

17 / 84 page

CC2400

SWRS042A

Page 17 of 83

16 Application Circuit

Few external components are required for

the

operation

CC2400. A typical

application circuit is shown in Figure 3. A

description of the external components

referring to Figure 3 are described in

Table 10. The bill of materials (BOM) is

given in Table 11.

Good PCB layout is vital for proper

operation, please see the section on PCB

Layout Recommendations on page 56 for

more details.

16.1 Input / output matching

The RF input/output is high impedance

and differential. The optimum differential

load for the RF port is listed on page 8.

When using an unbalanced antenna like a

monopole, a balun should be used in

order to get optimum performance. The

balun can be implemented using low-cost

discrete inductors and capacitors. The

balun consists of C61, C62, C71, C81,

L61, L62 and L72, and will match the RF

input/output to 50

Ω, see Figure 3. L61

and L62 also provide DC biasing of the

LNA/PA input/output. L71 is used to

isolate

the

TXRX_SWITCH

pin.

internal T/R switch circuit is used to switch

between the LNA and the PA. See

“Input/output matching” on page 50 for

more details.

If a balanced antenna, like a folded dipole,

is used, the balun can be omitted. If the

antenna also provides a DC path from the

TXRX_SWITCH pin to the RF pins,

inductors are not needed for DC biasing.

The L71 isolation inductor should still be

used to avoid antenna reflections. Figure 4

shows a typical application circuit with

differential antenna. The dipole has a

virtual ground point, hence bias is

provided without degradation in antenna

performance.

Please

note

that

differential antenna is generally larger than

an equivalent single-ended antenna.

16.2 Bias resistor

The bias resistor R451 is used to set an

accurate bias current for the chip.

16.3 Crystal

An external crystal with input and output

loading capacitors (C421 and C431) is

used for the crystal oscillator. See page 49

for details.

16.4 Digital I/O

The supply voltage for the digital I/O must

match the interfacing microcontroller. The

digital I/Os of

CC2400 can interface

microcontrollers with supply voltages in

the range 1.6 – 3.6 V.

16.5 Power supply decoupling and

filtering

Proper power supply decoupling must be

used for optimum performance. The

placement and size of the decoupling

capacitors and the power supply filtering

are very important to achieve the best

performance in an application. Chipcon

provides a compact reference design that

should be followed very closely.

16.6 Power supply switching

As described in a note in the Absolute

Maximum Ratings section, the voltage

supply to the chip core should not be

switched off separately from the I/O supply

voltage.

If it is necessary to switch the core power

supply off, for instance to save the power

dissipated in the 1.8V regulator, the I/O

supply should be turned off as well. This

can be done quite easily by running the

I/O supply from a microcontroller I/O pin.

Current drawn on the I/O supply is just a

few milliamps, so an ordinary I/O pin

should have no problems in sourcing this

current. Power sequencing should be

performed so that both supplies are turned

on and off simultaneously.

CC2400-RTR1 数据表(PDF) 17 Page - Texas Instruments

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