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AD7746:  24-bit, 2 Channel Capacitance to Digital Converter

Product Details


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 fea-tures 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-to-capacitance converter (CAPDAC).

The AD7745 has one capacitance input channel, while the AD7746 has two channels. Each channel can be configured as single-ended or differential. The AD7745/AD7746 are designed for floating capacitive sensors. For capacitive sensors with one plate connected to ground, the AD7747 is recommended.

The parts have 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 parts have a standard voltage input, which together with the differential reference input allows easy interface to an external temperature sensor, such as an RTD, thermistor, or diode.

The AD7745/AD7746 have a 2-wire, I2C-compatible serial interface. Both parts can operate with a single power supply from 2.7 V to 5.25 V. They are specified over the automotive temperature range of –40°C to +125°C and are housed in a 16-lead TSSOP package.

Applications

Automotive, Industrial and Medical Systems for:

  • Pressure Measurement
  • Position Sensors
  • Level Sensors
  • Flowmeters
  • Humidity Sensors
  • Impurity Detection

FEATURES and BENEFITS

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

Functional Block Diagram for AD7746

Documentation

Title Content Type File Type
AD7745/AD7746: 24-Bit Capacitance to Digital Converter with Temperature Sensor Data Sheet (Rev 0, 05/2005) (pdf, 773 kB) Data Sheets PDF
AN-1055: EMC Protection of the AD7746  (pdf, 464 kB) Application Notes PDF
CN-0129: Extending the Capacitive Input Range of the AD7745/AD7746 Capacitance-to-Digital Converter  (pdf, 134 kB) Circuit Note PDF
Webcast: Design And Develop Innovative And Robust Touch Sensor Interfaces Using Capacitive-To-Digital Converters
This Webcast will focus on the design and development of CDC-based touch sensors and their application, cite CDC product examples such as the AD7142, and explore development tools provided by ADI.
Webcasts WEBCAST
Boost Precision and Accuracy with Single Chip Capacitance- and Impedance-to-Digital Converters
(Analog Dialogue, Vol. 41, August, 2007)
Analog Dialogue HTML
Capacitance Sensors for Human Interfaces to Electronic Equipment
(Analog Dialogue, Vol. 40, October, 2006)
Analog Dialogue HTML
MS-2210: Designing Power Supplies for High Speed ADC  (pdf, 327 kB) Technical Articles PDF
Capacitance Sensors for Human Interfaces to Electronic Equipment
(Analog Dialogue, Vol. 40, October, 2006)
Technical Articles HTML
Delta-Sigma Rocks RF, As ADC Designers Jump On Jitter
(Electronic Design, 1/12/06)
Technical Articles HTML
ADI Rolls Out Single-chip Converters for Precise Capacitance and Impedance Measurements
(Automotive Design Line, 3/4/2005)
Product Reviews HTML
Capacitance And Impedance Converters—A High-Precision “First”
(Electronic Design Europe, 4/2005)
Product Reviews HTML
ADI Rolls Out Single-Chip Converters for Precise Capacitance and Impedance Measurements
(eeProductCenter, 3/2005)
Product Reviews HTML
Motion Sensing Devices Make Integrated Systems Easy
(Electropages, 11/24/2006)
Product Reviews HTML
2008 Medical Solution Profile  (pdf, 126 kB)
High Performance ICs for Medical Imaging, Patient Monitoring, and Instrumentation
Overview PDF
AD7150 Capacitance Converter for Proximity Sensing  (pdf, 1907 kB) Overview PDF
Capacitance-to-Digital Converter (CDC) Technology Overview HTML
Leading Inside Advertorials: Providing an Edge in Capacitive Sensor Applications  (pdf, 85 kB) Overview PDF
Leading Inside Advertorials: Boost Precision and Accuracy with Single Chip Capacitance- and Impedance-to-Digital Converters  (pdf, 482 kB) Overview PDF
What are Capacitive Sensors and how are they used? FAQs/RAQs HTML
RAQs index Rarely Asked Questions HTML
Glossary of EE Terms Glossary HTML

Design Tools,Models,Drivers & Software

Title Content Type File Type
AD7746 - Microcontroller No-OS Driver Device Drivers HTML
AD7746 IIO Capacitance to Digital Converter Linux Driver Device Drivers HTML

Evaluation Kits & Symbols & Footprints

Evaluation Boards & KitsView the Evaluation Boards and Kits page for documentation and purchasing

Symbols and Footprints— Analog Devices offers Symbols & Footprints which are compatible with a large set of today’s CAD systems for broader and easier support.

Product Recommendations & Reference Designs

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Price, packaging, availability

AD7746 Model Options
Model Package Pins Temp.
Range
Packing,
Qty
Price*(100-499) Price*1000 pcs RoHS View PCN/ PDN Check Inventory/
Purchase/Sample
AD7746ARUZ Status: Production 16 ld TSSOP 16 Ind Tube, 96 $5.92 $5.01 Y  Material Info PCN Purchase Sample
AD7746ARUZ-REEL Status: Production 16 ld TSSOP 16 Ind Reel, 2500 - $5.01 Y  Material Info PCN Purchase
AD7746ARUZ-REEL7 Status: Production 16 ld TSSOP 16 Ind Reel, 1000 - $5.01 Y  Material Info PCN Purchase
Price Table Help

The USA list pricing shown is for BUDGETARY USE ONLY, shown in United States dollars (FOB USA per unit for the stated volume), and is subject to change. International prices may differ due to local duties, taxes, fees and exchange rates. For volume-specific price or delivery quotes, please contact your local Analog Devices, Inc. sales office or authorized distributor. Pricing displayed for Evaluation Boards and Kits is based on 1-piece pricing.

AD7746 Evaluation Kit
Model Description Price RoHS View PCN/ PDN Check Inventory/
Purchase/Sample
EVAL-AD7746EBZ Status: Production Evaluation Board $59.00 Yes -

Pricing displayed is based on 1-piece. The USA list pricing shown is for budgetary use only, shown in United States dollars (FOB USA per unit), and is subject to change. International prices may vary due to local duties, taxes, fees and exchange rates.

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