®

INA103

11

12

7

5

RG

16

15

13

14

6

2

1

INA103

V

OUT

R

F

11 10

R

F

G = 1+

2R

R

G

F

NOTE: AD625 equivalent pinout.

VIN

∆

R

F > 10kΩ can increase noise and reduce bandwidth—see text.

FIGURE 7. Gain Adjustment of Output Stage.

FIGURE 8. Use of External Resistors for Gain Set.

OUTPUT STAGE

R1 and R3

R2

GAIN

(k

Ω)(Ω)

2

1k

2.4k

5

1.2k

632

Ω

10

1.2k

273

Ω

(R2 || 12k) + R1 + R3

(R2 || 12k)

Output Stage Gain =

11

10

7

16

15

13

14

6

2

1

INA103

VOUT

R3

R2

R1

∆VIN

A common problem with many IC op amps and instrumentation amplifiers is shown in (a). Here, the amplifier’s input is driven beyond its linear common-mode

range, forcing the output of the amplifier into the supply rails. The output then “folds back”, i.e., a more positive input voltage now causes the output of the amplifier

to go negative. The INA103 has protection circuitry to prevent fold-back, and as shown in (b), limits cleanly.

(a) AD625 G = 1, V

IN

=

±15V, R

L

= 600

Ω

(b) INA103 G = 1, V

IN

=

±15V, R

L

= 600

Ω

FIGURE 9. INA103 Overload Condition Performance.

11

10

7

VIN

16

15

13

14

6

2

1

INA103

∆

VOUT

RG

V+

V–

MJ15012

100

MJ15011

(To headphone

or speaker)

Buffer inside feedback loop

Ω

11

10

7

16

15

13

14

6

2

1

INA103

20

Ω

CMR

Trim

10

Ω

∆VIN

Gain = 1V/V

(0dB)

Introduces

approximately

+0.2% Gain Error.

FIGURE 11. Increasing Output Circuit Drive.

FIGURE 10. Optional Circuit for Externally Trimming CMR.