AD9239 datasheet(37/40 Pages) AD

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AD9239

Rev. 0 | Page 37 of

Power and Ground Recommendations

When connecting power to the AD9239, it is recommended

that two separate 1.8 V supplies be used: one for analog (AVDD)

and one for digital (DRVDD). If only one supply is available, it

should be routed to the AVDD first and then tapped off and

isolated with a ferrite bead or a filter choke preceded by

decoupling capacitors for the DRVDD. The user can employ

several different decoupling capacitors to cover both high and

low frequencies. These should be located close to the point of

entry at the printed circuit board (PCB) level and close to the

parts, with minimal trace lengths.

A single PCB ground plane should be sufficient when using the

AD9239. With proper decoupling and smart partitioning of the

analog, digital, and clock sections of the PCB, optimum

performance can easily be achieved.

Exposed Paddle Thermal Heat Slug Recommendations

It is required that the exposed paddle on the underside of the

ADC is connected to analog ground (AGND) to achieve the best

electrical and thermal performance of the AD9239. An exposed

continuous copper plane on the PCB should mate to the AD9239

exposed paddle, Pin 0. The copper plane should have several vias

to achieve the lowest possible resistive thermal path for heat

dissipation to flow through the bottom of the PCB. These vias

should be solder-filled or plugged with nonconductive epoxy.

To maximize the coverage and adhesion between the ADC and

PCB, partition the continuous copper plane by overlaying a

silkscreen on the PCB into several uniform sections. This provides

several tie points between the ADC and PCB during the reflow

process, whereas using one continuous plane with no partitions

guarantees only one tie point. See Figure 79 for a PCB layout

example. For detailed information on packaging and the PCB

layout of chip scale packages, see the AN-772 Application Note,

A Design and Manufacturing Guide for the Lead Frame Chip

Scale Package (LFCSP), at www.analog.com.

SILKSCREEN PARTITION

PIN 1 INDICATOR

Figure 79. Typical PCB Layout

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