AD8555 Datasheet, PDF (1/28 Pages) Analog Devices – Zero-Drift, Digitally Programmable Sensor Signal Amplifier

Zero-Drift, Digitally Programmable
Sensor Signal Amplifier
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
Automotive sensors
Pressure and position sensors
Thermocouple amplifiers
Industrial weigh scales
Precision current sensing
Strain gages
VNEG
VPOS
FUNCTIONAL BLOCK DIAGRAM
VDD
VDD
A1
VSS
VDD
A2
VSS
R4 ^P3 R6
R1
VDD
P1
R3
A3
P2
R2
R5
VSS
R7
VDD ^P4
VCLAMP
A5
VSS
VDD
RF
A4
FILT/
DIGOUT
VSS
DAC
VOUT
VSS
Figure 1.
GENERAL DESCRIPTION
The AD8555 is a zero-drift, sensor signal amplifier with digi-
tally 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 pat-
ented 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 off-
set 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 AD8555AR 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. 0
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