50kW

150kW

150kW

A

1

A

3

V

OUT

V

IN-

6

REF

5

RFIFilteredInputs

2

V+

7

V-

4

1

8

150kW

150kW

50kW

A

2

V

IN+

RFIFilteredInputs

3

INA333

R

G

G=1+

100kW

R

G

RFIFilteredInputs

RFIFilteredInputs

13

INA333

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SBOS445C – JULY 2008 – REVISED DECEMBER 2015

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7 Detailed Description

7.1 Overview

The INA333 is a monolithic instrumentation amplifier (INA) based on the precision zero-drift OPA333 (operational

amplifier) core. The INA333 also integrates laser-trimmed resistors to ensure excellent common-mode rejection

and low gain error. The combination of the zero-drift amplifier core and the precision resistors allows this device

to achieve outstanding DC precision and makes the INA333 ideal for many 3.3-V and 5-V industrial applications.

7.2 Functional Block Diagram

7.3 Feature Description

The INA333 is a low-power, zero-drift instrumentation amplifier offering excellent accuracy. The versatile three-

operational-amplifier design and small size make the amplifiers ideal for a wide range of applications. Zero-drift

chopper circuitry provides excellent DC specifications. A single external resistor sets any gain from 1 to 10,000.

The INA333 is laser trimmed for very high common-mode rejection (100 dB at G

≥ 100). This devices operate

with power supplies as low as 1.8 V, and quiescent current of 50 µA, typically.

7.4 Device Functional Modes

7.4.1 Internal Offset Correction

INA333 internal operational amplifiers use an auto-calibration technique with a time-continuous 350-kHz

operational amplifier in the signal path. The amplifier is zero-corrected every 8 µs using a proprietary technique.

Upon power up, the amplifier requires approximately 100 µs to achieve specified VOS accuracy. This design has

no aliasing or flicker noise.

7.4.2 Input Common-Mode Range

The linear input voltage range of the input circuitry of the INA333 is from approximately 0.1 V below the positive

supply voltage to 0.1 V above the negative supply. As a differential input voltage causes the output voltage to

increase, however, the linear input range is limited by the output voltage swing of amplifiers A1 and A2. Thus, the

linear common-mode input range is related to the output voltage of the complete amplifier. This behavior also

depends on supply voltage—see Figure 20.

Input overload conditions can produce an output voltage that appears normal. For example, if an input overload

condition drives both input amplifiers to the respective positive output swing limit, the difference voltage

measured by the output amplifier is near zero. The output of the INA333 is near 0 V even though both inputs are

overloaded.