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