Zero-Drift, Digitally Programmable

Sensor Signal Amplifier

Data Sheet

AD8555

FEATURES

Very low offset voltage: 10 µV maximum over temperature

Very low input offset voltage drift: 60 nV/°C maximum

High CMRR: 96 dB minimum

Digitally programmable gain and output offset voltage

Single-wire serial interface

Open and short wire fault detection

Low-pass filtering

Stable with any capacitive load

Externally programmable output clamp voltage for driving

low voltage ADCs

LFCSP-16 and SOIC-8 packages

2.7 V to 5.5 V operation

−40°C to +125°C operation

APPLICATIONS

Pressure and position sensors

Thermocouple amplifiers

Industrial weigh scales

Precision current sensing

Strain gages

FUNCTIONAL BLOCK DIAGRAM

A3

A2

A4

A5

VDD

VDD

DAC

VSS

VSS

VDD

VSS

VDD

VDD

VSS

VCLAMP

VPOS

VSS

FILT/

DIGOUT

VOUT

A1

VDD

VSS

VNEG

R1

R3

R2

R5

R7

P4

R4

R6

RF

P3

P2

P1

Figure 1.

GENERAL DESCRIPTION

The AD8555 is a zero-drift, sensor signal amplifier with

digitally programmable gain and output offset. Designed to

easily and accurately convert variable pressure sensor and strain

bridge outputs to a well-defined output voltage range, the

AD8555 also accurately amplifies many other differential or

single-ended sensor outputs. The AD8555 uses the ADI

patented low noise auto-zero and DigiTrim® technologies to

create an incredibly accurate and flexible signal processing

solution in a very compact footprint.

Gain is digitally programmable in a wide range from 70 to 1,280

through a serial data interface. Gain adjustment can be fully

simulated in-circuit and then permanently programmed with

proven and reliable poly-fuse technology. Output offset voltage

is also digitally programmable and is ratiometric to the supply

voltage.

In addition to extremely low input offset voltage and input

offset voltage drift and very high dc and ac CMRR, the AD8555

also includes a pull-up current source at the input pins and a

pull-down current source at the VCLAMP pin. This allows

open wire and shorted wire fault detection. A low-pass filter

function is implemented via a single low cost external capacitor.

Output clamping set via an external reference voltage allows the

AD8555 to drive lower voltage ADCs safely and accurately.

When used in conjunction with an ADC referenced to the same

supply, the system accuracy becomes immune to normal supply

voltage variations. Output offset voltage can be adjusted with a

resolution of better than 0.4% of the difference between VDD

and VSS. A lockout trim after gain and offset adjustment

further ensures field reliability.

The AD8555 is fully specified over the extended industrial

temperature range of −40°C to +125°C. Operating from single-

supply voltages of 2.7 V to 5.5 V, the AD8555 is offered in the

narrow 8-lead SOIC package and the 4 mm × 4 mm 16-lead

LFCSP.

Rev. B

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