AD9259 datasheet(33/52 Pages) AD

33 / 52 page

AD9259

Rev. 0 | Page 33 of 52

Power and Ground Recommendations

When connecting power to the AD9259, 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 PC board level and close to the parts with minimal

trace length.

A single PC board ground plane should be sufficient when

using the AD9259. 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 AD9259. An

exposed continuous copper plane on the PCB should mate to

the AD9259 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

silkscreen 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 ADC and PCB. See Figure 60 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 60. Typical PCB Layout

AD9259 Datasheet(PDF) 33 Page - Analog Devices