8

®

INA145

APPLICATION INFORMATION

The INA145 is a programmable gain difference amplifier

consisting of a gain of 1 difference amplifier and a program-

mable-gain output buffer stage. Basic circuit connections are

shown in Figure 1. Power supply bypass capacitors should

be connected close to pins 4 and 7, as shown. The amplifier

is programmable in the range of G = 1 to G = 1000 with two

external resistors.

The output of A1 is connected to the noninverting input of

A2 through a 10k

Ω resistor which is trimmed to ±1%

absolute accuracy. The A2 input is available for applications

such as a filter or a precision current source. See application

figures for examples.

OPERATING VOLTAGE

The INA145 is fully specified for supply voltages from

±2.25V to ±18V, with key parameters guaranteed over the

temperature range –40

°C to +85°C. The INA145 can be

operated with single or dual supplies, with excellent perfor-

mance. Parameters that vary significantly with operating

voltage, load conditions, or temperature are shown in the

typical performance curves.

SETTING THE GAIN

The gain of the INA145 is set by using two external

resistors, RG1 and RG2, according to the equation:

G = 1 + RG2/RG1

For a total gain of 1, A2 is connected as a buffer amplifier

with no RG1. A feedback resistor, RG2 = 10kΩ, should be

used in the buffer connection. This provides bias current

cancellation (in combination with internal R5) to assure

specified offset voltage performance. Commonly used val-

ues are shown in the table of Figure 1. Resistor values for

other gains should be chosen to provide a 10k

Ω parallel

resistance.

COMMON-MODE RANGE

The input resistors of the INA145 provides an input com-

mon-mode range that extends well beyond the power supply

rails. Exact range depends on the power supply voltage and

the voltage applied to the Ref terminal (pin 1). To assure

proper operation, the voltage at the non-inverting input of

A1 (an internal node) must be within its linear operating

range. Its voltage is determined by the simple 1:1 voltage

divider between pin 3 and pin 1. This voltage must be

between V– and (V+) – 1V.

FIGURE 1. Basic Circuit Connections.

A1

V

IN

INA145

V

O

R

2

40k

Ω

R

1

40k

Ω

V

IN

R

3

40k

Ω

R

4

40k

Ω

R

G1

R

G2

R

B

A2

V

01

7

3

2

5

41

8

6

–V

S

+V

S

0.1

µF

–

+

TOTAL GAIN

A2 GAIN

R

G1

R

G2

R

B

(V/V)

(V/V)

(W)

(W)

(W)

1

1

(None)

10k

—

2

2

20k

20k

—

5

5

12.4k

49.9k

—

10

10

11.0k

100k

—

20

20

10.5k

200k

—

50

50

10.2k

499k

—

100

100

10.2k

1M

—

200

200

499

100k

9.53k

500

500

100

49.9k

10k

1000

1000

100

100k

10k

STANDARD 1% RESISTORS

0.1

µF

V

O = (VIN – VIN)(1 + RG2/RG1)

+–

R

5

10k

Ω

(1%)