AD9271 datasheet(41/58 Pages) AD

41 / 58 page

Preliminary Technical Data

AD9271

Rev. PrA | Page 41 of 58

Power and Ground Recommendations

When connecting power to the AD9271, it is recommended

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

and one for digital (DRVDD). The AD9271 also requires a

3.3 V supply (CWVDD) as well for the crosspoint section. If

only one 1.8 V 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 should employ several decoupling capacitors

on all supplies to cover both high and low frequencies. These

should be located close to the point of entry at the PC board

level and close to the parts with minimal trace lengths.

A single PC board ground plane should be sufficient when

using the AD9271. With proper decoupling and smart parti-

tioning of the PC board’s analog, digital, and clock sections,

optimum performance is easily 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 AD9271. An

exposed continuous copper plane on the PCB should mate to

the AD9271 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.

To maximize the coverage and adhesion between the ADC and

PCB, partition the continuous copper plane by overlaying a silk-

screen on the PCB into several uniform sections. This provides

several tie points between the two during the reflow process. Using

one continuous plane with no partitions only guarantees one tie

point between the AD9271 and PCB. See Figure 64 for a PCB

layout example. For more detailed information on packaging

and the PCB layout, see the AN-772 Application Note.

SILKSCREEN PARTITION

PIN 1 INDICATOR

Figure 64. Typical PCB Layout

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