MAX4194(1999) Ver la hoja de datos (PDF) - Maxim Integrated

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MAX4194
(Rev.:1999)

Micropower, Single-Supply, Rail-to-Rail, Precision Instrumentation Amplifiers

Maxim Integrated 

Micropower, Single-Supply, Rail-to-Rail,

Precision Instrumentation Amplifiers

Table 1. MAX4194 External Gain Resistor

Selection

GAIN (V/V)

CLOSEST RG (1%) CLOSEST RG (5%)

(Ω)

(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

+100

511

510

+200

249

240

+500

100

100

+1,000

49.9

51

+2,000

24.9

24

+5,000

10

10

+10,000

4.99

5.1

* Leave pins 1 and 8 open for G = +1V/V.

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 nec-

essary to produce the associated VOUT. For the higher

gain configurations, the VCM range will increase at the

endpoints (B, C, E, and F) since a smaller differential

voltage 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.

5

MAX4194/MAX4195

G = +1V/V

4 REF = +2.5V/+1.5V

A

VCC = +5V/+3V

VEE = 0

TA = +25°C

3

B

F

2

C

E

1

0.03

0

0

D

1

2

3

OUTPUT VOLTAGE (V)

4.97

4

5

Figure 4. Common-Mode Input Voltage vs. Output Voltage

MAX4195

OUT

AC-COUPLED

(VDIFF = 2V,

G = +1V/V)

(500mV/div)

50µs/div

Figure 5a. MAX4195 Shutdown Mode

SHDN

(5V/div)

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