AD5322ARMZ datasheet(20/24 Pages) AD

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AD5302/AD5312/AD5322

Rev. D | Page 20 of 24

COARSE AND FINE ADJUSTMENT USING THE

AD5302/AD5312/AD5322

The DACs in the AD5302/AD5312/AD5322 can be paired

together to form a coarse and fine adjustment function, as

shown in Figure 44. DAC A is used to provide the coarse

adjustment while DAC B provides the fine adjustment. Varying

the ratio of R1 and R2 changes the relative effect of the coarse

and fine adjustments. With the resistor values and external

reference shown, the output amplifier has unity gain for the

DAC A output, so the output range is 0 V to 2.5 V − 1 LSB. For

DAC B, the amplifier has a gain of 7.6 × 10–3, giving DAC B a

range equal to 19 mV.

The circuit is shown with a 2.5 V reference, but reference

voltages up to VDD can be used. The op amps indicated allow a

rail-to-rail output swing.

GND

AD5302/AD5312/

AD5322

EXT

REF V

OUT

VOUTB

VREFA

1µF

GND

VIN

0.1µF

10µF

VDD

VDD = 5V

+5V

AD820/

OP295

VOUTA

VREFB

51.2kΩ

390Ω

VOUT

900Ω

51.2kΩ

Figure 44. Coarse/Fine Adjustment

POWER SUPPLY BYPASSING AND GROUNDING

In any circuit where accuracy is important, careful considera-

tion of the power supply and ground return layout helps to

ensure the rated performance. The printed circuit board on

which the AD5302/AD5312/AD5322 is mounted should be

designed so that the analog and digital sections are separated

and confined to certain areas of the board. If the AD5302/

AD5312/AD5322 are 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 AD5302/AD5312/

AD5322. The part should have ample supply bypassing of 10 μF

in parallel with 0.1 μF on the supply located as close as possible

to the package, 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), similar to the common ceramic types

that provide a low impedance path to ground at high frequencies

that handle transient currents due to internal logic switching.

The power supply lines of the AD5302/AD5312/AD5322

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. 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. 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 dedi-

cated to ground while signal traces are placed on the solder side.

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