MAX4195ESA datasheet(10/13 Pages) MAXIM

10 / 13 page

MAX4194–MAX4197

Micropower, Single-Supply,

Rail-to-Rail, Precision

Instrumentation Amplifiers

Maxim Integrated | 10

www.maximintegrated.com

VCM vs. VOUT 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 VCC = +5V and a bias reference voltage of

VREF = VCC/2 = +2.5V. Points A and D show the full

input voltage range of the input amplifiers (VEE - 0.2V to

VCC - 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 VOUT. For the higher gain

configurations, the VCM 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 VCC/2) resis-

tive load and still typically swing within 30mV of the

rails. With an output load of 5kΩ tied to VCC/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 / RG

where G is the instrumentation amplifier’s gain and RG

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.

345

OUTPUT VOLTAGE (V)

0.03

4.97

MAX4194/MAX4195

G = +1V/V

REF = +2.5V/+1.5V

VCC = +5V/+3V

VEE = 0

TA = +25

°C

SHDN

(5V/div)

MAX4195

OUT

AC-COUPLED

(VDIFF = 2V,

G = +1V/V)

(500mV/div)

μs/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 RG (1%)

(Ω)

CLOSEST RG (5%)

(Ω)

∞ *

49.9k

51k

12.4k

12k

+10

5.62k

5.6k

+20

2.61k

2.7k

+50

1.02k

1.0k

+100

511

510

+200

249

240

+500

100

+1,000

49.9

+2,000

24.9

+5,000

+10,000

4.99

5.1

Table 1. MAX4194 External Gain

Resistor Selection

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