CC2500-RTY1 datasheet(51/99 Pages) TI1

51 / 99 page

CC2500

SWRS040C

Page 51 of 89

Zout = 80 + j74 Ω

To ensure optimal matching of the

CC2500

differential output it is highly recommended to

follow the CC2500EM reference designs [4] as

closely as possible. Gerber files for the

reference designs are available for download

from the TI website.

28 PCB Layout Recommendations

The top layer should be used for signal

routing, and the open areas should be filled

with metallization connected to ground using

several vias.

The area under the chip is used for grounding

and shall be connected to the bottom ground

plane with several vias for good thermal

performance and sufficiently low inductance to

ground. In the CC2500EM reference designs

[4] 5 vias are placed inside the exposed die

attached pad. These vias should be “tented”

(covered with solder mask) on the component

side of the PCB to avoid migration of solder

through the vias during the solder reflow

process.

The solder paste coverage should not be

100%. If it is, out gassing may occur during the

reflow process, which may cause defects

(splattering, solder balling). Using “tented” vias

reduces the solder paste coverage below

100%.

See Figure 28 for top solder resist and top

paste masks. See Figure 30 for recommended

PCB layout for QLP 20 package.

Each decoupling capacitor should be placed

as close as possible to the supply pin it is

supposed

decouple.

Each

decoupling

capacitor should be connected to the power

line by separate vias. The best routing is from

the power line to the decoupling capacitor and

then to the

CC2500 supply pin. Supply power

filtering is very important.

Each decoupling capacitor ground pad should

be connected to the ground plane using a

separate via.

Direct connections between

neighboring power pins will increase noise

coupling

and

should

avoided

unless

absolutely necessary.

The external components should ideally be as

small as possible (0402 is recommended) and

surface

mount

devices

are

highly

recommended. Please note that components

smaller

than

those

specified

may

have

differing characteristics.

Precaution should be used when placing the

microcontroller

order

avoid

noise

interfering with the RF circuitry.

A CC2500/2550DK Development Kit with a

fully

assembled

CC2500EM

Evaluation

Module is available. It is strongly advised that

this reference layout is followed very closely in

order to get the best performance. The

schematic, BOM and layout Gerber files are all

available from the TI website [4].

Figure 28: Left: Top Solder Resist Mask (negative). Right: Top Paste Mask. Circles are Vias.

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