INA331, INA2331

SBOS215B

9

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APPLICATIONS INFORMATION

The INA331 is a modified version of the classic “two op amp”

instrumentation amplifier, with an additional gain amplifier.

Figure 1 shows the basic connections for the operation of the

INA331 and INA2331. The power supply should be capaci-

tively decoupled with 0.1

µF capacitors as close to the INA331

as possible for noisy or high-impedance applications.

The output is referred to the reference terminal, which must

be at least 1.2V below the positive supply rail.

OPERATING VOLTAGE

The INA331 family is fully specified over a supply range of

+2.7V to +5.5V, with key parameters tested over the tempera-

ture range of –55

°C to +125°C. Parameters that vary signifi-

cantly with operating conditions, such as load conditions or

temperature, are shown in the Typical Characteristics.

The INA331 may be operated on a single supply. Figure 2

shows a bridge amplifier circuit operated from a single +5V

supply. The bridge provides a small differential voltage riding

on an input common-mode voltage.

FIGURE 2. Single-Supply Bridge Amplifier.

FIGURE 1. Basic Connections.

40k

Ω

10k

Ω

10k

Ω

40k

Ω

3

2

5

1

7

8

4

Also drawn in simplified form:

6

REF

0.1

µF

0.1

µF

RG

V

V

V–

V+

A1

A3

A2

V

Short V

for G = 5

5

10

50

100

SHORT

100k

Ω

90k

Ω

190k

Ω

OPEN

100k

Ω

10k

Ω

10k

Ω

R

2

R

1

Shutdown

(For Single

Supply)

DESIRED GAIN

(V/V)

R

1

R

2

G = 5 + 5 (R

INA331

5

3

2

V

OUT

8

7

6

4

1

V+

Shutdown

RG

V

V–

V

REF

Bridge

Sensor

+5V

NOTE: (1) REF should be adjusted for the desired output level,

keeping in mind that the value of REF affects the common-mode

input range. See Typical Characteristics.

INA331

5

3

2

V

OUT

8

7

6

4

1

V+

Shutdown

RG

V

V–

V