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REV. 0

AD5334/AD5335/AD5336/AD5344

–18–

Coarse and Fine Adjustment Using the AD5334/AD5335/

AD5336/AD5344

Two of the DACs in the AD5334/AD5335/AD5336/AD5344 can

be paired together to form a coarse and ﬁne adjustment function,

as shown in Figure 39. As with the window comparator previ-

ously described, the description will refer to DACs A, and B and

the reference connections will depend on the actual device used.

DAC A is used to provide the coarse adjustment while DAC B

provides the ﬁne adjustment. Varying the ratio of R1 and R2 will

change the relative effect of the coarse and ﬁne adjustments. With

the resistor values shown the output ampliﬁer has unity gain for

the DAC A output, so the output range is zero to (VREF – 1 LSB).

For DAC B the ampliﬁer has a gain of 7.6

× 10–3, giving DAC B

a range equal to 2 LSBs of DAC A.

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

ages up to VDD may be used. The op amps indicated will allow a

rail-to-rail output swing.

GND

VDD = 5V

EXT

REF

AD780/REF192

WITH VDD = 5V

VIN

VOUT

51.2k

VOUT

0.1 F

10 F

AD5336/AD5344

GND

VREFA

VDD

VOUTA

390

VREFB

VOUTB

390

51.2k

Figure 39. Coarse and Fine Adjustment

Power Supply Bypassing and Grounding

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

AD5334/AD5335/AD5336/AD5344 is mounted should be

designed so that the analog and digital sections are separated,

and conﬁned to certain areas of the board. If the device 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 closely as pos-

sible to the device. The AD5334/AD5335/AD5336/AD5344

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 imped-

ance path to ground at high frequencies to handle transient

currents due to internal logic switching.

The power supply lines of the device 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 sig-

nals 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 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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