Zero Drift, Digitally Programmable

Instrumentation Amplifier

AD8231

Rev. 0

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FEATURES

Digitally/pin programmable gain

G = 1, 2, 4, 8, 16, 32, 64, 128

Specified from −40°C to +125°C

50 nV/°C maximum input offset drift

10 ppm/°C maximum gain drift

Excellent dc performance

80 dB minimum CMR, G = 1

15 μV maximum input offset voltage

500 pA maximum bias current

0.7 μV p-p noise (0.1 Hz to 10 Hz)

Good ac performance

2.7 MHz bandwidth, G = 1

1.1 V/μs slew rate

Rail-to-rail input and output

Shutdown/multiplex

Extra op amp

Single supply range: 3 V to 6 V

Dual supply range: ±1.5 V to ±3 V

APPLICATIONS

Pressure and strain transducers

Thermocouples and RTDs

Programmable instrumentation

Industrial controls

Weigh scales

FUNCTIONAL BLOCK DIAGRAM

IN-AMP

LOGIC

NC

1

–INA

2

+INA

3

NC

4

12

11

OUTA

10

REF

9

OP

AMP

AD8231

Figure 1.

Table 1. Instrumentation/Difference Amplifiers by Category

High

Performance

Low

Cost

High

Voltage

Mil

Grade

Low

Power

Digital

Gain

AD8221

AD6231

AD628

AD620

AD6271

AD82311

AD82201

AD85531

AD629

AD621

AD8250

AD8222

AD524

AD8251

AD82241

AD526

AD85551

AD624

AD85561

AD85571

GENERAL DESCRIPTION

The AD8231 is a low drift, rail-to-rail, instrumentation ampli-

fier with software programmable gains of 1, 2, 4, 8, 16, 32, 64, or

128. The gains are programmed via digital logic or pin

strapping.

The AD8231 is ideal for applications that require precision

performance over a wide temperature range, such as industrial

temperature sensing and data logging. Because the gain setting

resistors are internal, maximum gain drift is only 10 ppm/°C.

Because of the auto-zero input stage, maximum input offset is

15 μV and maximum input offset drift is just 50 nV/°C. CMRR

is also guaranteed over temperature at 80 dB for G = 1, increas-

ing to 110 dB at higher gains.

The AD8231 also includes an uncommitted op amp that can be

used for additional gain, differential signal driving or filtering.

Like the in-amp, the op amp has an auto-zero architecture, rail-

to-rail input, and rail-to-rail output.

The AD8231 includes a shutdown feature that reduces current

to a maximum of 1 μA. In shutdown, both amplifiers also have

a high output impedance. This allows easy multiplexing of

multiple amplifiers without additional switches.

The AD8231 is specified over the extended industrial tempera-

ture range of −40°C to +125°C. It is available in a 4 mm × 4 mm

16-lead LFCSP (chip scale).