ADL5246ACPZN-R7 datasheet(28/36 Pages) AD

28 / 36 page

ADL5246

Data Sheet

Rev. A | Page 28 of 36

THERMAL INFORMATION AND RECOMMENDED

PCB LAND PATTERN

The majority of the heat generated during operation is removed via

the exposed paddle on the bottom of the package. Figure 81 shows

the recommended land pattern for the ADL5246. To minimize

thermal impedance, the exposed paddle on the 5 mm × 5 mm

LFCSP package is soldered down to a ground plane. To improve

thermal dissipation, 25 thermal vias are arranged in a 5 × 5 array

under the exposed paddle. The land pattern on the ADL5246

evaluation board provides a thermal resistance (θJA) of 16.5°C/W.

For the best thermal performance, add as many thermal vias as

possible under the exposed pad of the LFCSP. If multiple ground

layers exist, tie them together using vias. For more information

on land pattern design and layout, see the AN-772 Application

Note, A Design and Manufacturing Guide for the Lead Frame

Chip Scale Package (LFCSP).

25 mils

12 mils

19.69

mils

12.0

mils

35 mils

16.46 mils

192.92

mils

122.0 mils

137.8 mils

Figure 81. Recommended Land Pattern Under ADL5246

FULL CHAIN OPERATION CONSIDERATIONS

The gain of a cascaded series of amplifiers may differ from a simple

summation of the gain of each amplifier in the chain due to

impedance matching considerations.

Take the following precautions in the PCB layout of a full chain

connection of AMP1 driving AMP2 driving AMP3:

•

The VPOS2 pin may couple RF from the three amplifiers into

AMP2 and lead to instability. Therefore, it is recommended

that the VPOS2 trace be well shielded from the other

amplifiers. To accomplish this with the ADL5246 evaluation

board, the VPOS2 trace passes through a via to the bottom

side of the PCB close to Pin 28.

•

At frequencies below 1.5 GHz, there can be more than 40 dB

of gain from the full chain connection. With so much gain

available, take care to maintain stable operation. Coupling

from trace to trace on the PCB can be a significant factor

leading to instability. Minimizing coupling between the

amplifiers through good PCB layout is important. It can be

helpful to reduce the overall gain with resistance before AMP3

(such as R10 on the evaluation board) or to include filters

or attenuators between the amplifiers.

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