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.
|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|
|CN-0108: Weigh Scale Design Using the AD7781 20-Bit Sigma-Delta ADC with Internal PGA (pdf, 775 kB)||Circuit Note|
|UG-079: Evaluation Board for the AD7781 20-Bit, Pin-Programmable, Low Power, Sigma-Delta ADC (pdf, 658 kB)||User Guides|
|MS-2210: Designing Power Supplies for High Speed ADC (pdf, 327 kB)||Technical Articles|
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)
|Test & Instrumentation Solutions Bulletin, Volume 10, Issue 3 (pdf, 1334 kB)||Solutions Bulletins|
|RAQs index||Rarely Asked Questions||HTML|
|Glossary of EE Terms||Glossary||HTML|
|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|
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.