MAX4209 Maxim, MAX4209 Datasheet - Page 13

• Manufacturer Part Number: MAX4209
• Description: The MAX4208/MAX4209 ultra-low offset and drift instrumentation amplifiers feature exceptional precision specifications, low power consumption, rail-to-rail output, excellent gain-bandwidth product, and buffered REFIN/MODE input in a very small &micro
• Manufacturer: Maxim

Connect a resistive divider from OUT to REF with the cen-
ter tap connected to FB to set the gain for the MAX4208
(see the Typical Application Circuit). Calculate the gain
using the following formula:
Choose a value for R1 ≤ 1kΩ. Resistor accuracy ratio
directly affects gain accuracy. Resistor sum less than
10kΩ should not be used because their loading can
slightly affect output accuracy.
Traditional three-op amp instrumentation amplifiers
have a defined relationship between the maximum
input differential voltage and maximum input common-
mode voltage that arises from saturation of intermediate
amplifier stages. This correlation is frequently repre-
sented as a hexagon graph of input common-mode
voltage vs. output voltage for the instrumentation ampli-
fier shown in Figure 3. Application limitations hidden in
this graph are:
• The input common-mode voltage range does not
• Input differential voltages can be amplified with
• If large amplitude common-mode voltages need to
The indirect current-feedback architecture of the
MAX4208/MAX4209 instrumentation amplifiers do not
suffer from any of these drawbacks. Figure 4 shows the
input common-mode voltage vs. output voltage graph
of indirect current-feedback architecture.
In contrast to three-op amp instrumentation amplifiers,
the MAX4208/MAX4209 features:
include the negative supply rail, and so no amplifi-
cation is possible for inputs near ground for single-
supply applications.
maximum gain only over a limited range of input
common-mode voltages (i.e., range of y-axis for max
range of x-axis is limited).
be rejected, differential voltages cannot be amplified
with a maximum gain possible (i.e., range of x-axis
for a maximum range of y-axis is limited). As a con-
sequence, a secondary high-gain amplifier is
required to follow the front-end instrumentation
amplifier.
Instrumentation Amplifiers with REF Buffer
Input Differential-Voltage Range
Applications Information
GAIN
______________________________________________________________________________________
Setting the Gain (MAX4208)
Input Common Mode vs.
=
1
+
⎛
⎜
⎝
R
R
2
1
⎞
⎟
⎠
Ultra-Low Offset/Drift, Precision
• The input common-mode voltage range, which
• Input differential voltages that can be amplified with
• Large common-mode voltages that can be rejected
Adjustable gain instrumentation amplifiers typically use a
single external resistor to set the gain. However, due to
differences in temperature drift characteristics between
the internal and external resistors, this leads to large
gain-accuracy drift over temperature. The MAX4208 is
an adjustable gain instrumentation amplifier that uses
two external resistors to set its gain. Since both resistors
are external to the device, layout and temperature coeffi-
cient matching of these parts deliver a significantly more
stable gain over operating temperatures.
The fixed gain, MAX4209H has both internal resistors for
excellent matching and tracking.
Zero-drift chopper amplifiers include circuitry that con-
tinuously compensates the input offset voltage to deliver
precision and ultra-low temperature drift characteristics.
This self-correction circuitry causes a small additional
noise contribution at its operating frequency (a psuedo-
random clock around 45kHz for MAX4208/MAX4209).
For high-bit resolution ADCs, external filtering can signif-
icantly attenuate this additional noise. Simply adding a
feedback capacitor (C
reduces high-frequency gain, while retaining the excel-
lent precision DC characteristics. Recommended values
for C
ing filtering at the output can further reduce this auto-
correction noise.
The MAX4208/MAX4209 are capable of driving capaci-
tive loads up to 200pF. Applications needing higher
capacitive drive capability may use an isolation resistor
between OUT and the load to reduce ringing on the
output signal. However, this reduces the gain accuracy
due to the voltage drop across the isolation resistor.
includes the negative supply rail and is ideal for sin-
gle-supply applications.
maximum gain over the entire range of input com-
mon-mode voltages.
at the same time differential voltages are amplified
with maximum gain, and therefore, no secondary
amplifier is required to follow the front-end instru-
mentation amplifier.
FB
are between 1nF and 10nF. Additional anti-alias-
Gain Error Drift Over Temperature
Use of External Capacitor C
Capacitive-Load Stability
FB
) between OUT and FB
for Noise Reduction
FB
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