7

®

INA132

APPLICATIONS INFORMATION

Figure 1 shows the basic connections required for operation

of the INA132. Power supply bypass capacitors should be

connected close to the device pins.

The differential input signal is connected to pins 2 and 3 as

shown. The source impedances connected to the inputs must

be nearly equal to assure good common-mode rejection. An

8

Ω mismatch in source impedance will degrade the com-

mon-mode rejection of a typical device to approximately

80dB. Gain accuracy will also be slightly affected. If the

source has a known impedance mismatch, an additional

resistor in series with one input can be used to preserve good

common-mode rejection.

Do not interchange pins 1 and 3 or pins 2 and 5, even though

nominal resistor values are equal. These resistors are laser

trimmed for precise resistor ratios to achieve accurate gain

and highest CMR. Interchanging these pins would not pro-

vide specified performance. As shown in Figure 1, measure-

ments should be sensed at the load.

supply ground). Although input voltages on pins 2 and 3

that are below the negative supply voltage will not damage

the device, operation in this region is not recommended.

Transient conditions at the inverting input terminal below

the negative supply can cause a positive feedback condition

that could lock the INA132’s output to the negative rail.

The INA132 can accurately measure differential signals that

are above the positive power supply. Linear common-mode

range extends to nearly twice the positive power supply

voltage—see typical performance curve, Common-Mode

Range vs Output Voltage.

OFFSET VOLTAGE TRIM

The INA132 is laser trimmed for low offset voltage and drift.

Most applications require no external offset adjustment.

Figure 2 shows an optional circuit for trimming the output

offset voltage. The output is referred to the output reference

terminal (pin 1), which is normally grounded. A voltage

applied to the Ref terminal will be summed with the output

signal. This can be used to null offset voltage. The source

impedance of a signal applied to the Ref terminal should be

less than 8

Ω to maintain good common-mode rejection. To

assure low impedance at the Ref terminal, the trim voltage

can be buffered with an op amp, such as the OPA177.

CAPACITIVE LOAD DRIVE CAPABILITY

The INA132 can drive large capacitive loads, even at low

supplies. It is stable with a 10,000pF load. Refer to the

“Small-Signal Step Response” and “Settling Time vs Load

Capacitance” typical performance curves.

FIGURE 1. Basic Power Supply and Signal Connections.

OPERATING VOLTAGE

The INA132 operates from single (+2.7V to +36V) or dual

(

±1.35V to ±18V) supplies with excellent performance.

Specifications are production tested with +5V and

±15V

supplies. Most behavior remains unchanged throughout the

full operating voltage range. Parameters which vary signifi-

cantly with operating voltage are shown in the typical

performance curves.

The internal op amp in the INA132 is a single-supply design.

This allows linear operation with the op amp’s common-

mode voltage equal to, or slightly below V– (or single

FIGURE 2. Offset Adjustment.

V

3

5

6

3

V

O

INA132

V

Offset Adjustment

Range = ±500µV

2

R

3

Ref

R

1

R

2

R

4

V

2

8

Ω

R = 237k

Ω

8

Ω

100k

Ω

+15V

–15V

1

NOTE: For ±750µV range, R = 158k

Ω.

V

3

5

6

3

INA132

V

2

R

3

Ref

R

1

R

2

R

4

V

2

40k

Ω

40k

Ω

40k

Ω

40k

Ω

R

L

1µF

V–

4

1µF

V+

7

1