INA166

6

SBOS178

FIGURE 2. Input Stabilization Network.

APPLICATIONS INFORMATION

Figure 1 shows the basic connections required for operation.

Power supplies should be bypassed with 0.1

µF tantalum capaci-

tors near the device pins. The output Sense (pin 8) and output

Reference (pin 10) should be low-impedance connections. Re-

sistance of greater than 5

Ω in series with these connections will

degrade the common-mode rejection of the INA166.

GAIN

Gain of the INA166 is internally set for G = 2000. Input stage

(A1, A2) gain is 200 and the output stage gain (A3) is 10.

Internal resistor values are laser trimmed for accurate ratios to

achieve excellent gain accuracy and common-mode rejection,

but absolute resistor values are approximately

±20%. Nominal

resistor values are shown.

Although the INA166 is primarily intended for fixed-gain

applications, the gain can be increased by connecting a gain-

set resistor, RG, between pin 3 and pin 12 The nominal gain

will be:

G

R

G

=+

2000

60000

Accuracy of the 60000 term in this equation is approxi-

mately

±20%. The stability and temperature drift of R

G

contributes to the overall gain accuracy and these effects can

be inferred from this gain equation.

NOISE PERFORMANCE

The INA166 provides very low-noise with low-source im-

pedance. Its 1.3nV/

√Hz voltage noise delivers near-theoreti-

cal noise performance with a source impedance of 200

Ω.

FIGURE 1. Basic Circuit Connections.

The input stage design used to achieve this low noise, results

in relatively high input bias current and input bias current

noise. As a result, the INA166 may not provide the best

noise performance with a source impedance greater than

10k

Ω. For source impedance greater than 10kΩ, other in-

strumentation amplifiers may provide improved noise per-

formance.

INPUT CONSIDERATIONS

Very low source impedance (less than 10

Ω) can cause the

INA166 to oscillate. This depends on circuit layout, signal

source, and input cable characteristics. An input network

consisting of a small inductor and resistor, as shown in

Figure 2, can greatly reduce any tendency to oscillate. This

is especially useful if a variety of input sources are to be

connected to the INA166. Although not shown in other

figures, this network can be used as needed with all applica-

tions shown.

V+

V–

V

O

11

6

V

IN

–

V

IN

+

INA166

47

Ω

47

Ω

1.2

µH

1.2

µH

8

4

3

12

5

10

11

6

9

A1

A2

A3

6k

Ω

60k

Ω

Sense

8

9

10

14

6

111

4

3

12

5

6k

Ω

60k

Ω

V

IN

–

+

V

IN

R

G

V+

V–

V+

V–

INA166

G = 2000

3k

Ω

3k

Ω

V

O

V

O

Sometimes Shown in

Simplified Form:

Ref

0.1

µF

0.1

µF

INA166

NOTE: Gain is internally set to G = 2000.

R

G can be used to increase gain. See text.

30.3

Ω