®

INA120

8

(a)

(b)

R

1

G

440

Ω

200

110

Ω

500

44k

Ω

R

G = 1 +

A

3

A

1

A

2

1

18

–V

2

12

7

6

3

4

5

8

9

10

11

17

13

16

15

14

IN

+V

IN

Ω

R = 816

for G = 50

G

Ω

R = 40k

G – 1

G

V

O

V+

V–

20k

Ω

20k

Ω

A

3

A

1

A

2

1

18

–V

2

12

7

6

3

4

5

8

9

10

11

17

13

16

15

14

IN

+V

IN

V

O

V+

V–

R

1

20k

Ω

20k

Ω

FIGURE 3. External Gain-Setting Resistors.

INPUT BIAS CURRENT RETURN PATH

The input impedance of the INA120 is extremely high—

Ω. This does not mean, however, that no

current flows in the input terminals. The input bias current

of the INA120 is typically

±10nA (it can be either polarity).

High input impedance means that this input bias current

changes very little with varying input voltage.

Input circuitry must provide a path for this input bias current

if the INA120 is to function. Figure 5 shows various provi-

sions for an input bias current path. Without an appropriate

current path, the inputs will float to a potential which

exceeds the common-mode range of the INA120 and the

input amplifiers will saturate.

INPUT PROTECTION

The inputs of the INA120 are protected for input voltages up

to 2V beyond the power supply voltages. If the input can

exceed these conditions, input clamp diodes should be pro-

vided as shown in Figure 6. R

input cannot supply more than 100mA. If the input can

supply larger currents, choose R

source voltage, limiting current to under 100mA.