INA321

INA2321

SBOS168B − DECEMBER 2000 − REVISED JULY 2004

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10

APPLICATIONS INFORMATION

The INA321 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 INA321 and INA2321. The power supply should be

capacitively decoupled with 0.1

µF capacitors as close to

the INA321 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 INA321 family is fully specified and guaranteed over

a supply range of +2.7V to +5.5V, with key parameters

guaranteed over the temperature range of −55

°C to

+125

°C. Parameters that vary significantly with operating

conditions, such as load conditions or temperature, are

shown in the Typical Characteristics.

The INA321 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.

160k

Ω

40k

Ω

40k

Ω

160k

Ω

3

2

5

1

7

8

4

Also drawn in simplified form:

6

REF

0.1

µF0.1µF

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

INA321

5

3

2

V

OUT

8

7

6

4

1

V+

Shutdown

RG

V

V

−

V

REF

Figure 1. Basic Connections

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.

INA321

5

3

2

V

OUT

8

7

6

4

1

V+

Shutdown

RG

V

V

−

V

Figure 2. Bridge Amplifier of the INA321