AD8021 datasheet(25/28 Pages) AD

25 / 28 page

AD7986

Rev. B | Page 25 of 28

APPLICATION HINTS

LAYOUT

The printed circuit board (PCB) that houses the AD7986 should

be designed so that the analog and digital sections are separated

and confined to certain areas of the board. The pinout of the

AD7986, with its analog signals on the left side and its digital

signals on the right side, eases this task.

Avoid running digital lines under the device because these couple

noise onto the die, unless a ground plane under the AD7986 is

used as a shield. Fast switching signals, such as CNV or clocks,

should not run near analog signal paths. Crossover of digital

and analog signals should be avoided.

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

split between the digital and analog sections. In the latter case,

the planes should be joined underneath the AD7986 devices.

The AD7986 voltage reference input, REF, has a dynamic input

impedance and should be decoupled with minimal parasitic induc-

tances. This is done by placing the reference decoupling ceramic

capacitor close to, ideally right up against, the REF and REFGND

pins and connecting them with wide, low impedance traces.

Finally, the power supplies, VDD and VIO of the AD7986,

should be decoupled with ceramic capacitors, typically 100 nF,

placed close to the AD7986 and connected using short, wide

traces to provide low impedance paths and to reduce the effect

of glitches on the power supply lines.

EVALUATING THE AD7986 PERFORMANCE

The evaluation board package for the AD7986 (EVAL-AD7986EB)

includes a fully assembled and tested evaluation board and soft-

ware for controlling the board from a PC via the converter

evaluation and development board, EVAL-CED1Z.

AD8021 Datasheet(PDF) 25 Page - Analog Devices