24-Bit Capacitance-to-Digital Converter with Temperature Sensor

The AD7747 is 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 19.5-bit effective resolution), high linearity (±0.01%), and high accuracy (±10 fF factory calibrated). The AD7747 capacitance input range is ±8 pF (changing), and it can accept up to 17 pF common-mode capacitance (not changing), which can be balanced by a programmable on-chip digital-to-capacitance converter (CAPDAC).

The AD7747 is designed for single-ended or differential capacitive sensors with one plate connected to ground. For floating (not grounded) capacitive sensors, the AD7745 or AD7746 are recommended.

The part has an on-chip temperature sensor with a resolution of 0.1°C and accuracy of ±2°C. The on-chip voltage reference and the on-chip clock generator eliminate the need for any external components in capacitive sensor applications. The part has a standard voltage input that, together with the differential reference input, allows easy interface to an external temperature sensor, such as an RTD, thermistor, or diode.

The AD7747 has a 2-wire, I2C-compatible serial interface. The part can operate with a single power supply of 2.7 V to 5.25 V. It is specified over the automotive temperature range of −40°C to +125°C and is housed in a 16-lead TSSOP package.

Applications

Automotive, industrial, and medical systems for:

* Pressure measurement

* Position sensing

* Proximity sensing

* Level sensing

* Flowmeters

* Impurity detections

* New standard in single chip solutions * Interfaces to single or differential grounded sensors * Resolution down to 20 aF (that is, up to 19.5-bit ENOB) * Accuracy: 10 fF * Linearity: 0.01% * Common-mode (not changing) capacitance up to 17 pF * Full-scale (changing) capacitance range ±8 pF * Update rate: 5 Hz to 45 Hz