AD8476 AD [Analog Devices], AD8476 Datasheet - Page 18

• Manufacturer Part Number: AD8476
• Description: Low Power, Unity Gain, Fully
• Manufacturer: AD [Analog Devices]

AD8476
The
trimmed to guarantee a minimum CMRR of 90 dB (32 μV/V),
and gain error of less that 0.02%. To achieve equivalent precision
and performance using a discrete solution, resistors must be
matched to 0.01% or better.
INPUT VOLTAGE RANGE
The
rails. The internal gain and feedback resistors form a divider,
which reduces the input voltage seen by the internal input
nodes of the amplifier. The largest voltage that can be measured
properly is constrained by the output range of the amplifier and
the capability of the amplifier’s internal summing nodes. This
voltage is defined by the input voltage, and the ratio between the
feedback and the gain resistors.
Figure 53 shows the voltage at the internal summing nodes of
the amplifier, defined by the input voltage and internal resistor
network. If V
The internal amplifier of the
To obtain accurate measurements with minimal distortion, the
voltage at the internal inputs of the amplifier must stay below
+V
The
voltages beyond the supply rails. Integrated ESD protection diodes
at the inputs prevent damage to the
and −V
S
AD8476
AD8476
− 1 V and above −V
AD8476
V
PLUS
S
− 18 V.
=
V
N
integrated resistors are precision wafer-laser-
can measure input voltages as large as the supply
provides overvoltage protection for excessive input
is grounded, the expression shown reduces to
MINUS
=
RF
S
.
RG
+
RG
AD8476



RF + RG
VOCM
RG
AD8476
has rail-to-rail inputs.
+
VOCM
Figure 53. Voltages at the Internal Op Amp Inputs of the
1
2
up to +V
RG
RF
+
1
2
V
RF
RG
P



S
V
+ 18 V
P
− V
N
Rev. B | Page 18 of 24
+
RF + RG
RF
V
N
DRIVING THE AD8476
Care should be taken to drive the
impedance source: for example, another amplifier. Source
resistance can unbalance the resistor ratios and, therefore,
significantly degrade the gain accuracy and common-mode
rejection of the AD8476. For the best performance, source
impedance to the
below 0.1 Ω. Refer to the DC Precision section for details on
the critical role of resistor ratios in the precision of the AD8476.
POWER SUPPLIES
The
can be powered on a single supply as low as 3 V and as high as
18 V. The
±1.5 V to ±9 V
A stable dc voltage should be used to power the AD8476. Note
that noise on the supply pins can adversely affect performance.
For more information, see the PSRR performance curve in
Figure 10.
Place a bypass capacitor of 0.1 μF between each supply pin and
ground, as close as possible to each supply pin. Use a tantalum
capacitor of 10 μF between each supply and ground. It can be
farther away from the supply pins and, typically, it can be
shared by other precision integrated circuits.
V
V
P
N
VOCM
AD8476
RG
RG
AD8476
operates over a wide range of supply voltages. It
AD8476
RF
RF
AD8476
can also operate on dual supplies from
V
V
ON
OP
input terminals should be kept
AD8476
with a low
Data Sheet