AD7746 Analog Devices Data Sheet Handbook

24-Bit Capacitance-to-Digital Converter

with Temperature Sensor

AD7745/AD7746

FEATURES GENERAL DESCRIPTION

Capacitance-to-digital converter

The AD7745/AD7746 are a high resolution, Σ-Δ capacitance-to-

New standard in single chip solutions

digital converter (CDC). The capacitance to be measured is

Interfaces to single or differential floating sensors

connected directly to the device inputs. The architecture fea-

Resolution down to 4 a F (that is, up to 21 ENOB)

tures inherent high resolution (24-bit no missing codes, up to

Accuracy: 4 f F

21-bit effective resolution), high linearity (±0.01%), and high

Linearity: 0.01%

accuracy (±4 f F factory calibrated). The AD7745/AD7746

Common-mode (not changing) capacitance up to 17 p F

capacitance input range is ±4 p F (changing), while it can accept

Full-scale (changing) capacitance range: ±4 p F

up to 17 p F common-mode capacitance (not changing), which

Tolerant of parasitic capacitance to ground up to 60 p F

Update rate: 10 Hz to 90 Hz can be balanced by a programmable on-chip, digital-to- Simultaneous 50 Hz and 60 Hz rejection at 16 Hz capacitance converter (CAPDAC).

Temperature sensor on-chip

The AD7745 has one capacitance input channel, while the

Resolution: 0.1°C, accuracy: ±2°C

AD7746 has two channels. Each channel can be configured as

Voltage input channel

single-ended or differential. The AD7745/AD7746 are designed

Internal clock oscillator 8-

for floating capacitive sensors. For capacitive sensors with one

2-wire serial interface (I2C®-compatible)

plate connected to ground, the AD7747 is recommended.

Power

2.7 V to 5.25 V single-supply operation The parts have an on-chip temperature sensor with a resolution 0.7 m A current consumption of 0.1°C and accuracy of ±2°C. The on-chip voltage reference Operating temperature: –40°C to +125°C and the on-chip clock generator eliminate the need for any

16-lead TSSOP package external components in capacitive sensor applications. The

parts have a standard voltage input, which together with the

APPLICATIONS www.BDTIC.com/A differential reference input allows easy interface to an external Automotive, industrial, and medical systems for temperature sensor, such as an RTD, thermistor, or diode. Pressure measurement

The AD7745/AD7746 have a 2-wire, I2C-compatible serial

Position sensing

interface. Both parts can operate with a single power supply

Level sensing

from 2.7 V to 5.25 V. They are specified over the automotive

Flowmeters

temperature range of –40°C to +125°C and are housed in a

Humidity sensing

16-lead TSSOP package.

Impurity detection

FUNCTIONAL BLOCK DIAGRAMS VDD VDD

TEMP CLOCK TEMP CLOCK

SENSOR GENERATOR AD7745 SENSOR GENERATOR AD7746

VIN(+) VIN(+) VIN(–) VIN(–)

I2C SDA I2C SDA

MUX 24-BIT Σ-∆ DIGITAL MUX 24-BIT Σ-∆ DIGITAL

CIN1(+) SERIAL CIN1(+) SERIAL

MODULATOR FILTER MODULATOR FILTER

CIN1(–) INTERFACE CIN1(–) INTERFACE

SCL SCL

CIN2(+)

8- CIN2(–)

CONTROL LOGIC CONTROL LOGIC

CAP DAC RDY CAP DAC RDY

CALIBRATION CALIBRATION

CAP DAC CAP DAC

VOLTAGE VOLTAGE EXCA EXCITATION REFERENCE EXC1 EXCITATION REFERENCE

EXCB EXC2

REFIN(+) REFIN(–) GND REFIN(+) REFIN(–) GND

Figure 1. Figure 2.

Rev. 0 Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use.

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