INA152

8

SBOS184

APPLICATIONS INFORMATION

The INA152 is a low-power difference amplifier suitable for

a wide range of general-purpose applications. Figure 1

shows the basic connections required for operation of the

INA152. Decoupling capacitors are strongly recommended

in applications with noisy or high-impedance power sup-

plies. The capacitors should be placed close to the device

pins, as shown in Figure 1.

As shown in Figure 1, the differential input signal is con-

nected to pins 2 and 3. 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 common-mode rejection of a typical device to

approximately 80dB (a 16

Ω mismatch degrades CMR to

74dB). If the source has a known impedance mismatch, an

additional resistor in series with the opposite input can be

used to preserve good common-mode rejection.

The INA152’s internal resistors are accurately ratio trimmed

to match. That is, R1 is trimmed to match R2, and R3 is

trimmed to match R4. However, the absolute values may not

be equal (R1 + R2 may be slightly different than R3 + R4).

Thus, large series resistors on the input (greater than 250

Ω),

even if well matched, will degrade common-mode rejection.

Circuit-board layout constraints might suggest possible varia-

tions in connections of the internal resistors. It might appear

that pins 1 and 3 could be interchanged, however, because of

the ratio trimming technique used (see paragraph above)

CMRR will be degraded. If pins 1 and 3 are interchanged,

pins 2 and 5 must also be interchanged to maintain proper

ratio matching.

OPERATING VOLTAGE

The INA152 operates from single (+2.7V to +20V) or dual

(

±1.35V to ±10V) supplies with excellent performance. Speci-

fications are production tested with +5V and

±10V supplies.

Most behavior remains unchanged throughout the full oper-

ating voltage range. Parameters that vary significantly with

operating voltage are shown in the typical performance

curves.

INPUT VOLTAGE

The INA152 can accurately measure differential signals that

are above and below the supply rails. Linear common-mode

range extends from 2 • [(V+) – 1V] to 2 • (V–) (nearly twice

the supplies). See the typical performance curve, “Input

Common-Mode Voltage vs Output Voltage”.

OFFSET VOLTAGE TRIM

The INA152 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, as shown in

Figure 2. The source impedance of a signal applied to the Ref

terminal should be less than 10

Ω to maintain good common-

mode rejection.

FIGURE 1. Precision Difference Amplifier (Basic Power

Supply and Signal Connections).

FIGURE 2. Offset Adjustment.

V

3

+In

5

6

1

3

INA152

V

O = V3 – V2

Gain Error =

±0.01%

CMR = 94dB

Nonlinearity =

±0.002%

2

R

3

40k

Ω

R

4

40k

Ω

R

1

40k

Ω

R

2

40k

Ω

V

2

–In

1

µF

V–

4

1

µF

V+

7

V

3

5

6

3

V

O

INA152

V

O = V3 – V2

Offset Adjustment

Range =

±1mV

2

R

3

R

1

R

2

R

4

V

2

10

Ω

100k

Ω

10

Ω

100k

Ω

+V

–V

1