GENERAL DESCRIPTION
The AD7745/AD7746 are a high resolution, Σ-Δ capacitance-to-digital converter (CDC). The capacitance to be measured is connected directly to the device inputs. The architecture features inherent high resolution (24-bit no missing codes, up to 21-bit effective resolution), high linearity (±0.01%), and high accuracy (±4 fF factory calibrated). The AD7745/AD7746 capacitance input range is ±4 pF (changing), while it can accept up to 17 pF common-mode capacitance (not changing), which can be balanced by a programmable on-chip, digital-tocapacitance converter (CAPDAC).

FEATURES
   Capacitance-to-digital converter
      New standard in single chip solutions
      Interfaces to single or differential floating sensors
      Resolution down to 4 aF (that is, up to 21 ENOB)
      Accuracy: 4 fF
      Linearity: 0.01%
      Common-mode (not changing) capacitance up to 17 pF
      Full-scale (changing) capacitance range: ±4 pF
      Tolerant of parasitic capacitance to ground up to 60 pF
      Update rate: 10 Hz to 90 Hz
      Simultaneous 50 Hz and 60 Hz rejection at 16 Hz
   Temperature sensor on-chip
      Resolution: 0.1°C, accuracy: ±2°C
   Voltage input channel
   Internal clock oscillator
   2-wire serial interface (I2C®-compatible)
   Power
      2.7 V to 5.25 V single-supply operation
      0.7 mA current consumption
   Operating temperature: –40°C to +125°C
   16-lead TSSOP package

APPLICATIONS
   Automotive, industrial, and medical systems for
      Pressure measurement
      Position sensing
      Level sensing
      Flowmeters
      Humidity sensing
      Impurity detection