ADR1581
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
impedance seen looking into the IOUT2 terminal changes with
DAC code. If the ADR1581 drives IOUT2 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.
USING THE ADR1±81 WITH 3 V DATA
CONVERTERS
The ADR1581 low output drift (50 ppm/°C) and compact
subminiature 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-
balancing (∑-Δ) 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. Figure 24 shows the ADR1581 connected to the
AD7714/AD7715 for 3 V operation.
3.3V
R
V
FB
DD
C1
I
I
OUT1
OUT2
V
REF
V
A1
DAC
V
IN
OUT
3V
AGND
A1: OP295
AD822
AD7943
DGND
28.7kΩ
OP2283
AD7714-3/AD7715-3
REF IN(+)
R
SW
5kΩ (TYP)
HIGH
IMPEDANCE
>1GΩ
ADR1581
REF IN(–)
C
REF
(3pF TO 8pF)
3.3V
SWITCHING
FREQUENCY DEPENDS
ON fCLKIN
29.4kΩ
A1
ADR1581
Figure 24. Reference Circuit for the AD7714-3/AD7715-3
SIGNAL GROUND
Figure 25. Single-Supply System
Rev. 0 | Page 10 of 12
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