Datasheet

MAX4194–MAX4197
Micropower, Single-Supply, Rail-to-Rail,
Precision Instrumentation Amplifiers
10 ______________________________________________________________________________________
V
CM
vs. V
OUT
Characterization
Figure 4 illustrates the MAX4194 typical common-mode
input voltage range over output voltage swing at unity-
gain (pins 1 and 8 left floating), with a single-supply
voltage of V
CC
= +5V and a bias reference voltage of
V
REF
= V
CC
/2 = +2.5V. Points A and D show the full
input voltage range of the input amplifiers (V
EE
- 0.2V to
V
CC
- 1.1V) since, with +2.5V output, there is zero input
differential swing. The other points (B, C, E, and F) are
determined by the input voltage range of the input
amps minus the differential input amplitude necessary
to produce the associated V
OUT
. For the higher gain
configurations, the V
CM
range will increase at the end-
points (B, C, E, and F) since a smaller differential volt-
age is necessary for the given output voltage.
Rail-to-Rail Output Stage
The MAX4194–MAX4197’s output stage incorporates a
common-source structure that maximizes the dynamic
range of the instrumentation amplifier.
The output can drive up to a 25kΩ (tied to V
CC
/2) resis-
tive load and still typically swing within 30mV of the
rails. With an output load of 5kΩ tied to V
CC
/2, the out-
put voltage swings within 100mV of the rails.
Shutdown Mode
The MAX4195–MAX4197 feature a low-power shutdown
mode. When the shutdown pin (SHDN) is pulled low,
the internal amplifiers are switched off and the supply
current drops to 8µA typically (Figures 5a, 5b, and 5c).
This disables the instrumentation amplifier and puts its
output in a high-impedance state. Pulling SHDN high
enables the instrumentation amplifier.
Applications Information
Setting the Gain (MAX4194)
The MAX4194’s gain is set by connecting a single,
external gain resistor between the two RG pins (pin 1
and pin 8), and can be described as:
G = 1 + 50kΩ / R
G
where G is the instrumentation amplifier’s gain and R
G
is the gain-setting resistor.
The 50kΩ resistor of the gain equation is the sum of the
two resistors internally connected to the feedback loops
of the IN+ and IN- amplifiers. These embedded feed-
back resistors are laser trimmed, and their accuracy
and temperature coefficients are included in the gain
and drift specification for the MAX4194.
0
1
3
2
4
5
021 345
OUTPUT VOLTAGE (V)
COMMON-MODE INPUT VOLTAGE (V)
B
C
0.03 4.97
D
A
F
E
MAX4194/MAX4195
G = +1V/V
REF = +2.5V/+1.5V
V
CC
= +5V/+3V
V
EE
= 0
T
A
= +25°C
SHDN
(5V/div)
MAX4195
OUT
AC-COUPLED
(V
DIFF
= 2V,
G = +1V/V)
(500mV/div)
50µs/div
Figure 4. Common-Mode Input Voltage vs. Output Voltage
Figure 5a. MAX4195 Shutdown Mode
*Leave pins 1 and 8 open for G = +1V/V.
GAIN (V/V)
CLOSEST R
G
(1%)
(Ω)
CLOSEST R
G
(5%)
(Ω)
+1 ∞ * ∞ *
+2 49.9k 51k
+5 12.4k 12k
+10 5.62k 5.6k
+20 2.61k 2.7k
+50 1.02k 1.0k
[phone]
[phone]
[phone]
+1,000 49.9 51
+2,000 24.9 24
+5,000 10 10
+10,000 4.99 5.1
Table 1. MAX4194 External Gain Resistor
Selection