AD8555_09 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
R1
P1
R3
P2
R2
R5
VDD
P3 _R6
VDD
A3
VSS
R7
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 digital-
ly 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 com-
pact 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 fur-
ther ensures field reliability.
The AD8555 is fully specified over the extended industrial tem-
perature 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. A
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