Datasheet

ADR1581
Rev. 0 | Page 10 of 12
USING THE ADR1581 WITH 3 V DATA
CONVERTERS
The ADR1581 is ideal for creating the reference level to use
with 12-bit multiplying DACs, such as the AD7943, AD7945,
and AD7948. In the single-supply bias mode (see Figure 25), the
im
pedance seen looking into the I
OUT2
terminal changes with
DAC code. If the ADR1581 drives I
OUT2
and AGND directly, less
than 0.2 LSBs of additional linearity error results. The buffer amp
eliminates linearity degradation resulting from variations in the
reference level.
The ADR1581 low output drift (50 ppm/°C) and compact
sub
miniature SOT-23 package make it ideally suited for today’s
high performance converters in space-critical applications.
One family of ADCs for which the ADR1581 is well suited is the
AD7714-3 and AD7715-3. The AD7714/AD7715 are charge-
bala
ncing (∑-∆) ADCs with on-chip digital filtering intended for
the measurement of wide dynamic range, low frequency signals,
such as those representing chemical, physical, or biological
processes.
DAC
R
FB
AGND
DGND
A1
C1
3.3
V
29.4kΩ
3.3V
ADR1581
SIGNAL GROUND
A1: OP295
AD822
OP2283
A1
V
REF
V
IN
V
DD
I
OUT1
I
OUT2
V
OUT
AD7943
06672-025
Figure 24 shows the ADR1581 connected to the
AD7714/AD7715 for 3 V operation.
AD7714-3/AD7715-3
A
DR1581
3
V
28.7kΩ
REF IN(+)
REF IN(–)
HIGH
IMPEDANCE
>1GΩ
R
SW
5kΩ (TYP)
C
REF
(3pF TO 8pF)
SWITCHING
FREQUENCY DEPENDS
ON
f
CLKIN
06672-024
Figure 24. Reference Circuit for the AD7714-3/AD7715-3
Figure 25. Single-Supply System