INA126PA.. datasheet(7/19 Pages) BURR-BROWN

7 / 19 page

INA126, INA2126

SBOS062A

www.ti.com

APPLICATION INFORMATION

Figure 1 shows the basic connections required for operation

of the INA126. Applications with noisy or high impedance

power supplies may require decoupling capacitors close to

the device pins as shown.

The output is referred to the output reference (Ref) terminal

which is normally grounded. This must be a low-impedance

connection to ensure good common-mode rejection. A resis-

tance of 8

Ω in series with the Ref pin will cause a typical

device to degrade to approximately 80dB CMR.

Dual versions (INA2126) have feedback sense connections,

SenseA and SenseB. These must be connected to their respec-

tive output terminals for proper operation. The sense con-

nection can be used to sense the output voltage directly at the

load for best accuracy.

SETTING THE GAIN

Gain is set by connecting an external resistor, RG, as shown:

(1)

Commonly used gains and RG resistor values are shown in

Figure 1.

The 80k

Ω term in equation 1 comes from the internal metal film

resistors which are laser trimmed to accurate absolute values.

The accuracy and temperature coefficient of these resistors are

included in the gain accuracy and drift specifications.

The stability and temperature drift of the external gain

setting resistor, RG, also affects gain. RG’s contribution to

gain accuracy and drift can be directly inferred from the gain

equation (1). Low resistor values required for high gain can

make wiring resistance important. Sockets add to the wiring

resistance, which will contribute additional gain error in

gains of approximately 100 or greater.

OFFSET TRIMMING

The INA126 and INA2126 are laser trimmed for low offset

voltage and offset voltage drift. Most applications require no

external offset adjustment. Figure 2 shows an optional cir-

cuit for trimming the output offset voltage. The voltage

applied to the Ref terminal is added to the output signal. An

op amp buffer is used to provide low impedance at the Ref

terminal to preserve good common-mode rejection.

FIGURE 1. Basic Connections.

DESIRED GAIN

NEAREST 1%

(V/V)

(

Ω)R

G VALUE

5NC

16k

15.8k

5333

5360

1779

1780

100

842

845

200

410

412

500

162

1000

80.4

80.6

2000

40.1

40.2

5000

16.0

15.8

10000

8.0

7.87

NC: No Connection.

=5 + 80

Ω

FIGURE 2. Optional Trimming of Output Offset Voltage.

10k

Ω

OPA237

±10mV

Adjustment Range

100

Ω

100

Ω

100µA

1/2 REF200

100µA

1/2 REF200

V+

V–

INA126

Ref

✻

–

✻ Dual version has

external sense connection.

40k

Ω

10k

Ω

10k

Ω

40k

Ω

INA126

–

V+

V–

INA126

0.1

µF

0.1

µF

Ref

✻

Ref

Load

–

Also drawn in simplified form:

O = (VIN – VIN) G

–

G = 5 +

✻

Pin numbers are

for single version

✻ Dual version has

external sense connection.

80k

Ω

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