AD7607 datasheet(30/32 Pages) AD

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AD7608

Data Sheet

Rev. A | Page 30 of 32

LAYOUT GUIDELINES

The printed circuit board that houses the AD7608 should be

designed so that the analog and digital sections are separated

and confined to different areas of the board.

Use at least one ground plane. 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 AD7608.

If the AD7608 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 should be

established as close as possible to the AD7608. Good connections

should be made to the ground plane. Avoid sharing one connec-

tion for multiple ground pins. Individual vias or multiple vias to

the ground plane should be used for each ground pin.

Avoid running digital lines under the devices because doing so

couples noise onto the die. Allow the analog ground plane to

run under the AD7608 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. Run traces on

layers in close proximity on the board 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 on the

AD7608 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. Good

connections should be made between the AD7608 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 to lower the supply impedance

presented to the AD7608 and to reduce 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 AD7608 pins and where possible

they should be placed on the same side of the board as the AD7608

device. Figure 59 shows the recommended decoupling on the

top layer of the AD7608 board. Figure 60 shows bottom layer

decoupling. Bottom layer decoupling is for the four AVCC pins

and the VDRIVE pin.

Figure 59. Top Layer Decoupling REFIN/REFOUT, REFCAPA, REFCAPB, and

REGCAP Pins

Figure 60. Bottom Layer Decoupling

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