AD5313 datasheet(17/20 Pages) AD

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REV. F

AD5305/AD5315/AD5325

–17–

1 F

REFIN

VDD

GND

VOUTB

0.1 F

10 F

VDD = 5V

VOUT

VIN

GND

EXT

REF

AD820/

OP295

51.2k

390

AD780/REF192

WITH VDD = 5V

VOUTA

390

51.2k

VOUT

1/2

AD5305/

AD5315/

AD5325*

*ADDITIONAL PINS OMITTED FOR CLARITY

Figure 15. Coarse/Fine Adjustment

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

AD5305/AD5315/AD5325 is mounted should be designed so

that the analog and digital sections are separated and conﬁned

to certain areas of the board. If the AD5305/AD5315/AD5325

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. The AD5305/AD5315/AD5325 should have ample

supply bypassing of 10

µF in parallel with 0.1 µF on the supply

located as close to the package as possible, ideally right up against

the device. The 10

µF capacitors are the tantalum bead type.

The 0.1

µF capacitor should have low effective series resistance

(ESR) and effective series inductance (ESI), like the common

ceramic types that provide a low impedance path to ground at

high frequencies, to handle transient currents due to internal

logic switching.

The power supply lines of the AD5305/AD5315/AD5325 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 signals such as clocks 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. A ground line

routed between the SDA and SCL lines will help reduce crosstalk

between them (not required on a multilayer board as there will

be a separate ground plane, but separating the lines will help).

Avoid crossover of digital and analog signals. Traces on oppo-

site sides of the board should run at right angles to each other.

This reduces the effects of feedthrough through the board. A

microstrip technique is by far the best, but is not always possible

with a double-sided board. In this technique, the component

side of the board is dedicated to ground plane while signal traces

are placed on the solder side.

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