Datasheet

AD7176-2 Data Sheet
Rev. A | Page 24 of 68
AD8475
The AD8475 features an attenuating input stage of 0.8× or 0.4×
(using integrated precision resistors), allowing inputs in the ±10 V
range with a single 5 V supply and a 3 mA current consumption
to be used. The AD8475 performs single-ended to differential
conversions, allows easy setting of the common-mode output,
and drives the AD7176-2 with a differential input.
Figure 30 shows a typical connection to the AD7176-2, where
two AD8475 amplifiers attenuate two differential inputs and
then drive the AD7176-2 inputs. The common-mode output of
the AD8475 is set by connecting the internal, buffered 2.5 V
reference of the AD7176-2 to the VOCM pin of the AD8475.
The output of the AD8475 to the AD7176-2 is fully differential
with a fixed common mode of 2.5 V. The output of the AD8475
amplifier is connected to an RC network. The RC network, as
shown in Figure 30, includes R
IN
= 10 Ω; C1, C2 = 270 pF; and
C3 = 680 pF. The RC circuit acts to provide the dynamic charge
required by the AD7176-2 switched sampling capacitors while
isolating the amplifier output from any kickback from the
dynamic switched capacitor input. The configuration of the
AD8475 in Figure 30 shows a fully differential signal source
with a gain of 0.4×.
The AD8475 can also be set up to convert single-ended signals
to fully differential inputs. Ground the −IN 0.4× input and
apply the single-ended input to the +IN 0.4× input.
Figure 30. AD8475 Driving Two Differential Inputs of the AD7176-2
AD8475
AD7176-2
±12.5V
LOW IMPEDANCE
VOLTAGE
SOURCE
IN0
R
IN
C1
0.1µF
C2
C3
R
IN
–IN 0.4x
+5V
+IN 0.4x
VOCM
IN1
AD8475
±12.5V
LOW IMPEDANCE
VOLTAGE
SOURCE
IN2
R
IN
C1
C2
C3
R
IN
+IN 0.4x
–IN 0.4x
VOCM
IN3
ADR445
MICROCONTROLLER
HOST
0.1µF
5V VREF
0.1µF
4.7µF
+5V
5.5V TO 18V
0.1µF
0.1µF
2.5V
0.1µF
2
6
3
REF–
AVSS
7
AVDD1
8
AVDD2*
*AVDD2 CAN BE SUPPLIED BY VOLTAGES RANGING FROM 2V TO 5.5V.
REF+
24
23
22
21
AIN0
AIN1
AIN2
4
REFOUT
AIN3
0.1µF
0.1µF
+5V
CS
11
12
13
14
DOUT/RDY
DIN
SCLK
11037-057