Auto Electronics

Digitally Programmable Sensor Signal Amplifier

Analog Devices' AD8556 is a zero-drift, sensor signal amplifier with digitally programmable gain and output offset. Designed to convert variable pressure sensor and strain bridge outputs to a well-defined output voltage range, the AD8556 accurately amplifies many other differential or single-ended sensor outputs. The AD8556 uses the ADI patented low noise auto-zero and DigiTrim technologies to create an accurate and flexible signal processing solution in a compact footprint. The amplifier is aimed at applications like automotive sensors, pressure and position sensors, precision current sensing, and strain gages.

Gain is digitally programmable in a wide range from 70 to 1,280 through a serial data interface. Gain adjustment can be simulated in-circuit and then permanently programmed with polyfuse technology. Output offset voltage is also digitally programmable and is ratiometric to the supply voltage. Additionally, the signal amplifier also features internal EMI filters on the VNEG, VPOS, FILT and VCLAMP pins.

In addition to low input offset voltage, low input offset voltage drift, and high dc and ac CMRR, the AD8556 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 unit 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. Fully specified from 40 °C to +140 °C, it operates from single-supply voltages of 2.7 V to 5.5 V and is offered in the eight-lead SOIC_N, and 4 mm 4 mm 16-lead LFCSP_VQ.
Analog Devices Inc. • (800) 262-5643www.analog.com

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