Datasheet

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.
V
REF
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 1M
ISOLATION (dB)
INPUT FREQUENCY (Hz)
V
DD
= +15V
V
SS
= –5V
T
A
= 25°C
V
REF
= 1.24V p-p
00986-014
Figure 14. Channel-to-Channel Isolation
V
OUT
CV
OUT
B
V
OUT
DV
OUT
A
V
DD
V
SS
V
REF
CV
REF
B
V
REF
DV
REF
A
MSB LSB
PIN 1
SYSTEM
GND
DGND
AGND
00986-015
Figure 15. Suggested PCB Layout for AD7225, Component Side (Top View)