Datasheet

MAX4194–MAX4197
Micropower, Single-Supply, Rail-to-Rail,
Precision Instrumentation Amplifiers
12 ______________________________________________________________________________________
Power-Supply Bypassing and Layout
Good layout technique optimizes performance by
decreasing the amount of stray capacitance at the
instrumentation amplifier’s gain-setting pins. Excess
capacitance will produce peaking in the amplifier’s fre-
quency response. To decrease stray capacitance, min-
imize trace lengths by placing external components as
close to the instrumentation amplifier as possible. For
best performance, bypass each power supply to
ground with a separate 0.1µF capacitor.
Transducer Applications
The MAX4194–MAX4197 instrumentation amplifiers can
be used in various signal-conditioning circuits for ther-
mocouples, PT100s, strain gauges (displacement sen-
sors), piezoresistive transducers (PRTs), flow sensors,
and bioelectrical applications. Figure 7 shows a simpli-
fied example of how to attach four strain gauges (two
identical two-element strain gauges) to the inputs of the
MAX4194. The bridge contains four resistors, two of
which increase and two of which decrease by the same
ratio.
With a fully balanced bridge, points A (IN+) and B (IN-)
see half the excitation voltage (V
BRIDGE
). The low
impedance (120Ω to 350Ω) of the strain gauges, how-
ever, could cause significant voltage drop contributions
by the wires leading to the bridge, which would cause
excitation variations. Output voltage V
OUT
can be cal-
culated as follows:
V
OUT
= V
AB
· G
where G = (1 + 50kΩ / R
G
) is the gain of the instrumen-
tation amplifier.
Since V
AB
is directly proportional to the excitation, gain
errors may occur.
Figure 7. Strain Gauge Connection to the MAX4194
IN-
V
EE
V
CC
V
AB
= V
IN+
- V
IN-
V
BRIDGE
R
R
R
R
R
G
IN+
RG+
RG-
OUT
REFERENCE
µP
REF
B
A
MAX144
ADC
R = 120Ω - 350Ω
___________________Chip Information
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