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AD7781:  20-Bit, Pin-Programmable, Ultralow Power Sigma-Delta ADC

Product Details


The AD7781 is a complete low power front-end solution for bridge sensor products, including weigh scales, strain gages, and pressure sensors. It contains a precision low power 20-bit sigma-delta (Σ-Δ) ADC, an on-chip, low noise programmable gain amplifier (PGA), and an on-chip oscillator.

Consuming only 330 μA, the AD7781 is particularly suitable for portable or battery-operated products where very low power is required. The AD7781 also has a power-down mode that allows the user to switch off the power to the bridge sensor and power down the AD7781 when not converting, thus increasing the battery life of the product.

For ease of use, all the features of the AD7781 are controlled by dedicated pins. Each time that a data read occurs, eight status bits are appended to the 20-bit conversion. These status bits contain a pattern sequence that can be used to confirm the validity of the serial transfer.

The on-chip PGA has a gain of 1 or 128, supporting a full-scale differential input of ±5 V or ±39 mV. The device has two filter response options. The filter response at the 16.7 Hz update rate provides superior dynamic performance. The settling time is 120 ms at this update rate. At the 10 Hz update rate, the filter response provides better than -45 dB of stop-band attenuation. In load cell applications, this stop-band rejection is useful to reject low frequency mechanical vibrations of the load cell. The settling time is 300 ms at this update rate. Simultaneous 50 Hz/60 Hz rejection occurs at both the 10 Hz and 16.7 Hz update rates.

The AD7781 operates with a power supply from 2.7 V to 5.25 V. It is available in a narrow body, 14-lead SOIC package and in a 16-lead TSSOP package.

Applications

  • Weigh scales
  • Pressure measurement
  • Industrial process control
  • Portable instrumentation

FEATURES and BENEFITS

  • Pin-programmable filter response
    Update rate: 10 Hz or 16.7 Hz
  • Pin-programmable in-amp gain
  • Pin-programmable power-down and reset
  • Status function
  • Internal clock oscillator
  • Internal bridge power-down switch
  • Current:
    115 μA typical (Gain = 1)
    330 μA typical (Gain = 128)
  • Simultaneous 50 Hz/60 Hz rejection
  • Please see data sheet for additional features

Functional Block Diagram for AD7781

Documentation

Title Content Type File Type
AD7781: 20-Bit, Pin-Programmable, Low Power Sigma-Delta ADC Data Sheet (Rev 0, 05/2009) (pdf, 387 kB) Data Sheets PDF
CN-0108: Weigh Scale Design Using the AD7781 20-Bit Sigma-Delta ADC with Internal PGA  (pdf, 775 kB) Circuit Note PDF
UG-079: Evaluation Board for the AD7781 20-Bit, Pin-Programmable, Low Power, Sigma-Delta ADC  (pdf, 658 kB) User Guides PDF
MS-2210: Designing Power Supplies for High Speed ADC  (pdf, 327 kB) Technical Articles PDF
High-resolution ADCs — an overview
The dramatic reduction in the cost of high-resolution ADCs brings a number of benefits to designers.
(Electronic Products, 4/23/2010)
Technical Articles HTML
Test & Instrumentation Solutions Bulletin, Volume 10, Issue 3  (pdf, 1334 kB) Solutions Bulletins PDF
RAQs index Rarely Asked Questions HTML
Glossary of EE Terms Glossary HTML

Design Tools,Models,Drivers & Software

Title Content Type File Type
Sigma-Delta ADC Tutorial
An interactive illustration showing the behavior of an idealized sigma-delta A/D converter.
Utilities and Conversions HTML
AD7780 IIO Low Power Sigma-Delta ADC Linux Driver (Wiki Site) 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.

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Price, packaging, availability

AD7781 Model Options
Model Package Pins Temp.
Range
Packing,
Qty
Price*(100-499) Price*1000 pcs RoHS View PCN/ PDN Check Inventory/
Purchase/Sample
AD7781BRUZ Status: Production 16 ld TSSOP 16 Ind Tube, 96 $4.95 $4.20 Y  Material Info PCN Purchase Sample
AD7781BRUZ-REEL Status: Production 16 ld TSSOP 16 Ind Reel, 2500 - $4.20 Y  Material Info PCN Purchase
AD7781BRZ Status: Production 14 ld SOIC 14 Ind Tube, 56 $4.95 $4.20 Y  Material Info PCN Purchase Sample
AD7781BRZ-REEL Status: Production 14 ld SOIC 14 Ind Reel, 2500 - $4.20 Y  Material Info PCN Purchase
AD7781CRUZ Status: Production 16 ld TSSOP 16 Ind Tube, 96 $5.20 $4.40 Y  Material Info PCN Purchase
AD7781CRUZ-REEL Status: Production 16 ld TSSOP 16 Ind Reel, 2500 - $4.40 Y  Material Info PCN Purchase
AD7781CRZ Status: Production 14 ld SOIC 14 Ind Tube, 56 $5.20 $4.40 Y  Material Info PCN Purchase
AD7781CRZ-REEL Status: Production 14 ld SOIC 14 Ind Reel, 2500 - $4.40 Y  Material Info Notify Me 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.

AD7781 Evaluation Board
Model Description Price RoHS View PCN/ PDN Check Inventory/
Purchase/Sample
EVAL-AD7781EBZ 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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