AD5522JSVDZ datasheet(41/45 Pages) AD

41 / 45 page

Preliminary Technical Data

AD5522

Rev. PrL | Page 41 of 45

POWER SUPPLY DECOUPLING

In any circuit where accuracy is important, careful

consideration of the power supply and ground return layout

helps to ensure the rated performance. The printed circuit

board on which the AD5522 is mounted should be designed so

that the analog and digital sections are separated and confined

to certain areas of the board. If the AD5522 is in a system where

multiple devices require an AGND-to-DGND connection, the

connection should be made at one point only. The star ground

point should be established as close as possible to the device.

For supplies with multiple pins (AVSS, AVDD, VCC), it is

recommended to tie these pins together and to decouple each

supply once.

The AD5522 should have ample supply decoupling of 10 µF in

parallel with 0.1 µF on each supply located as close to the

package as possible, ideally right up against the device. The

10µF capacitors are the tantalum bead type. The 0.1 µF

capacitor should have low effective series resistance (ESR) and

effective series inductance (ESI), such as the common ceramic

types that provide a low impedance path to ground at high

frequencies, to handle transient currents due to internal logic

switching.

Digital lines running under the device should be avoided,

because these couple noise onto the device. The analog ground

plane should be allowed to run under the AD5522 to avoid

noise coupling (only with the package with paddle up).. The

power supply lines of the AD5522 should use as large a trace as

possible to provide low impedance paths and reduce the effects

of glitches on the power supply line. Fast switching digital

signals should be shielded with digital ground to avoid

radiating noise to other parts of the board, and should never be

run near the reference inputs. It is essential to minimize noise

on all VREF lines. Avoid crossover of digital and analog signals.

Traces on opposite sides of the board should run at right angles

to each other. This reduces the effects of feedthrough through

the board. As is the case for all thin packages, care must be

taken to avoid flexing the package and to avoid a point load on

the surface of this package during the assembly process.

Also note that the exposed paddle of the AD5522 is connected

to the negative supply AVSS.

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