AD7225LPZ datasheet(11/24 Pages) AD

11 / 24 page

AD7225

Rev. C | Page 11 of 24

GROUND MANAGEMENT AND LAYOUT

Because the AD7225 contains four reference inputs that can be

driven from ac sources (see the AC Reference Signal section),

careful layout and grounding is important to minimize analog

crosstalk between the four channels. The dynamic performance

of the four DACs depends on the optimum choice of board

layout. Figure 14 shows the relationship between input fre-

quency and channel-to-channel isolation. Figure 15 shows a

printed circuit board layout that minimizes crosstalk and

feedthrough. The four input signals are screened by AGND.

VREF was limited to between 2 V and 3.24 V to avoid slew rate

limiting effects from the output amplifier during measurements.

–80

–70

–60

–50

–40

–30

20k

50k

100k

200k

500k

INPUT FREQUENCY (Hz)

VDD = +15V

VSS = –5V

TA = 25°C

VREF = 1.24V p-p

Figure 14. Channel-to-Channel Isolation

VOUTC

VOUTB

VOUTD

VOUTA

VDD

VSS

VREFC

VREFB

VREFD

VREFA

MSB

LSB

PIN 1

SYSTEM

GND

DGND

AGND

Figure 15. Suggested PCB Layout for AD7225, Component Side (Top View)

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