AD7607 datasheet(30/33 Pages) AD

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Data Sheet

AD7607

Rev. C | Page 29 of 32

LAYOUT GUIDELINES

The printed circuit board that houses the AD7607 should be

designed so that the analog and digital sections are separated

and confined to different areas of the board.

At least one ground plane should be used. It can be common or

split between the digital and analog sections. In the case of the

split plane, the digital and analog ground planes should be joined

in only one place, preferably as close as possible to the AD7607.

If the AD7607 is in a system where multiple devices require

analog-to-digital ground connections, the connection should

still be made at only one point: a star ground point that should be

established as close as possible to the AD7607. Good connections

should be made to the ground plane. Avoid sharing one connection

for multiple ground pins. Use individual vias or multiple vias to

the ground plane for each ground pin.

Avoid running digital lines under the devices because doing so

couples noise onto the die. The analog ground plane should be

allowed to run under the AD7607 to avoid noise coupling. Fast

switching signals like CONVST A, CONVST B, or clocks should

be shielded with digital ground to avoid radiating noise to other

sections of the board, and they should never run near analog

signal paths. Avoid crossover of digital and analog signals. Traces

on layers in close proximity on the board should run at right angles

to each other to reduce the effect of feedthrough through the board.

The power supply lines to the AVCC and VDRIVE pins should use

as large a trace as possible to provide low impedance paths and

reduce the effect of glitches on the power supply lines. Where

possible, use supply planes and make good connections between

the AD7607 supply pins and the power tracks on the board.

Use a single via or multiple vias for each supply pin.

Good decoupling is also important in lowering the supply

impedance presented to the AD7607 and in reducing the

magnitude of the supply spikes. The decoupling capacitors should

be placed close to (ideally, right up against) these pins and their

corresponding ground pins. Place the decoupling capacitors for

the REFIN/REFOUT pin and the REFCAPA and REFCAPB

pins as close as possible to their respective AD7607 pins; and,

where possible, they should be placed on the same side of the

board as the AD7607 device.

Figure 52 shows the recommended decoupling on the top layer

of the AD7607 board. Figure 53 shows bottom layer decoupling,

which is used for the four AVCC pins and the VDRIVE pin.

Figure 52. Top Layer Decoupling REFIN/REFOUT,

REFCAPA, REFCAPB, and REGCAP Pins

Figure 53. Bottom Layer Decoupling

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