MAX4194 Maxim, MAX4194 Datasheet - Page 9

• Manufacturer Part Number: MAX4194
• Description: The MAX4194 is a variable-gain precision instrumentation amplifier that combines Rail-to-Rail; single-supply operation, outstanding precision specifications, and a high gain bandwidth
• Manufacturer: Maxim

The MAX4194–MAX4197 family of low-power instru-
mentation amplifiers implements a three-amplifier topol-
ogy (Figure 1). The input stage is composed of two
operational amplifiers that together provide a fixed-gain
differential and a unity common-mode gain. The output
stage is a conventional differential amplifier that pro-
vides an overall common-mode rejection of 115dB (G =
Figure 1. MAX4194 Simplified Block Diagram
Figure 2. MAX4195/MAX4196/MAX4197 Simplified Block
Diagram
Figure 3. Instrumentation Amplifier Configuration
RG+
RG-
IN+
IN-
SHDN
V
IN+
IN-
IN+
- V
V
V
IN+
IN-
IN-
R
25kΩ
25kΩ
G
25kΩ
25kΩ
R
G
**
_______________________________________________________________________________________
Micropower, Single-Supply, Rail-to-Rail,
MAX4194
Detailed Description
I
I
25kΩ
25kΩ
G
G
MAX4195
MAX4196
MAX4197
25kΩ
25kΩ
Precision Instrumentation Amplifiers
A1
A2
R
R
1
1
*
*
25kΩ
25kΩ
V
V
OUT1
OUT2
25kΩ
25kΩ
Input Stage
V
OUT2
- V
OUT1
R
R
V
OUT
REF
V
2
2
*
*
CC
EE
V
FB
OUT
REF
V
CC
EE
R
R
+10V/V). The MAX4194’s gain can be externally set
between +1V/V and +10,000V/V (Table 1). The
MAX4195/MAX4196/MAX4197 have on-chip gain-set-
ting resistors (Figure 2), and their gains are fixed at
+1V/V, +10V/V, and +100V/V, respectively.
The common-mode input range for all of these ampli-
fiers is V
tation amplifier (Figure 3) responds only to a differential
voltage applied to its inputs, IN+ and IN-. If both inputs
are at the same voltage, the output is V
tial voltage at IN+ (V
identical voltage across the gain-setting resistor, caus-
ing a current (I
through the feedback resistors of the two input ampli-
fiers A1 and A2, generating a differential voltage of:
where V
and A2, R
nal to the part), and R1 is the feedback resistor of the
input amplifiers.
I
The output voltage (V
amplifier is expressed in the following equation:
The common-mode input range is a function of the
amplifier’s output voltage and the supply voltage. With
a power supply of V
can be obtained with REF tied to V
an output voltage swing of ±V
swing less than full-scale increases the common-mode
input range.
A3
G
2
2
*
*
is determined by the following equation:
V
OUT1
EE
OUT
V
G
OUT2
- 0.2V to V
V
is the gain-setting resistor (internal or exter-
OUT
OUT
REF
= (V
and V
= (V
- V
I
G
G
IN+
IN+
) to flow. This current also flows
** R
OUT1
= (V
- V
* R
OUT2
CC
R
IN-
1
G
G
- V
IN+
CC
= R
= INTERNAL TO MAX4195/MAX4196/MAX4197
= EXTERNAL TO MAX4194
)
, the largest output signal swing
IN+
·
OUT
2
IN-
= I
(
) and IN- (V
and Detailed Operation
= 25kΩ
1 +
- 1.1V. Ideally, the instrumen-
are the output voltages of A1
) · [(2 · R1) / R
G
- V
2R
) for the instrumentation
Input Voltage Range
R
· (R
G
1
IN-
CC
)
) / R
1
/2. An output voltage
+ R
CC
G
IN-
/2. This results in
G
REF
+ R
) develops an
G
] + 1
. A differen-
1
)
9