INA326, INA327

9

SBOS222D

www.ti.com

IA

COMMON

(2)

INA326

R

1

V

IN

−

V

IN+

V

V

O

6

2

1

8

3

G = 2(R

f

R

O

100

Ω

C

O

(1)

1

µF

R

2

C

2

(1)

7

+2.5V

4

0.1

µF

−2.5V

5

(1) C

Each individual pole is at 1.5kHz.

(2) Output voltage is referenced to IA

DESIRED

GAIN

(

0.1

400k

20k || 5

0.2

400k

40k || 2.5

0.5

400k

100k || 1

1

400k

200k || 0.5

2

200k

200k || 0.5

5

80k

200k || 0.5

10

40k

200k || 0.5

20

20k

200k || 0.5

50

8k

200k || 0.5

100

4k

200k || 0.5

200

2k

200k || 0.5

500

2k

500k || 0.2

1000

2k

1M || 0.1

2000

2k

2M || 0.05

5000

2k

5M || 0.02

10000

2k

10M || 0.01

APPLICATIONS INFORMATION

Figure 1 shows the basic connections required for operation of

the INA326. A 0.1

µF capacitor, placed close to and across the

power-supply pins is strongly recommended for highest accu-

circuitry noise. This output filter may also serve as an anti-

aliasing filter ahead of an Analog-to-Digital (A/D) converter. It

is also optional based on desired precision.

The INA326 uses a unique internal topology to achieve excel-

lent Common-Mode Rejection (CMR). Unlike conventional

instrumentation amplifiers, CMR is not affected by resistance

in the reference connections or sockets. See “Inside the

INA326” for further detail. To achieve best high-frequency

CMR, minimize capacitance on pins 1 and 8.

FIGURE 1. Basic Connections. NOTE: Connections for INA327 differ—see Pin Configuration for detail.

SETTING THE GAIN

The INA326 is a 2-stage amplifier with each stage gain set

for details). Overall gain is described by the equation:

G

R

R

1

(1)

The stability and temperature drift of the external gain-setting

resistors will affect gain by an amount that can be directly

inferred from the gain equation (1).

Resistor values for commonly used gains are shown in

Figure 1. Gain-set resistor values for best performance are

different for +5V single-supply and for

±2.5V dual-supply

(2)

DESIRED

GAIN

(

0.1

400k

20k || 5

0.2

400k

40k || 2.5

0.5

400k

100k || 1

1

200k

100k || 1

2

100k

100k || 1

5

40k

100k || 1

10

20k

100k || 1

20

10k

100k || 1

50

4k

100k || 1

100

2k

100k || 1

200

2k

200k || 0.5

500

2k

500k || 0.2

1000

2k

1M || 0.1

2000

2k

2M || 0.05

5000

2k

5M || 0.02

10000

2k

10M || 0.01

INA326

V

V

O

6

G = 2(R

f

R

O

100

Ω

C

O

(1)

1

µF

R

2

C

2

(1)

7

V+

4

0.1

µF

5

IA

COMMON

(2)

R

1

(1) C

Each individual pole is at 1.5kHz.

(2) Output voltage is referenced to IA

(3) Output offset voltage required for measurement near zero (see Figure 28).

Single-supply operation may require

R

This may produce higher input referred

offset voltage. See

Offset Voltage,

Drift, and Circuit Values for detail.

1

8

V

IN

−

V

IN+

2

3

(3)