Analog Devices: CN0216 Reference Design for Precision Weigh Scale Design Using the AD7791 24-Bit Sigma-Delta ADC with External ADA4528-1 Zero-Drift Amplifiers

atomar — Tue, 23 Apr 2013 08:00:31 GMT

Current Revision posted to Documents by atomar on 4/23/2013 8:00:31 AM

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Kit Overview

This Analog Devices Circuit Evaluation Board EVAL-CN0216-SDPZEVAL-CN0216-SDPZ is a precision weigh scale signal conditioning system. It uses the AD7791AD7791, a low power buffered 24-bit sigma-delta ADC along with two external ADA4528-1ADA4528-1 zero-drift amplifiers. This solution allows for high dc gain with a single supply. Ultralow noise, low offset voltage, and low drift amplifiers are used at the front end for amplification of the low-level signal from the load cell. The circuit yields 15.3 bit noise-free code resolution for a load cell with a full-scale output of 10 mV.

This circuit allows great flexibility in designing a custom low-level signal conditioning front end that gives the user the ability to easily optimize the overall transfer function of the combined sensor-amplifier-converter circuit. The AD7791AD7791 maintains good performance over the complete output data range, from 9.5 Hz to 120 Hz, which allows it to be used in weigh scale applications that operate at various low speeds.

The AD7791AD7791 is a low power, complete analog front end for low frequency measurement applications. It contains a low noise 24-bit Σ-Δ ADC with one differential input that can be buffered or unbuffered.

The ADA4528-1ADA4528-1 are ultralow noise, zero-drift operational amplifiers featuring rail-to-rail input and output swing. With an offset voltage of 2.5 μV, offset voltage drift of 0.015 μV/°C, and typical noise of 97 nV p-p (0.1 Hz to 10 Hz, AV = +100), the ADA4528-1 are well suited for applications in which error sources cannot be tolerated.

This circuit uses the EVAL-CN0216-SDPZEVAL-CN0216-SDPZ circuit board and the EVAL-SDP-CB1ZEVAL-SDP-CB1Z System Demonstration Platform (SDP-B) evaluation board. The two boards have 120-pin mating connectors, allowing for the quick setup and evaluation of the circuit’s performance. The EVAL-CN0216-SDPZ board contains the circuit to be evaluated and the SDP evaluation board is used with the CN-0216 evaluation software to capture the data from the EVAL-CN0216-SDPZ circuit board.

Key Applications: Weigh Scales

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Development Tools

PC with a USB port and Windows XP or Windows Vista (32-bit), or Windows 7 (32-bit)
EVAL-CN0216-SDPZEVAL-CN0216-SDPZ circuit evaluation board
EVAL-SDP-CB1ZEVAL-SDP-CB1Z SDP evaluation board
- Blackfin Processor ADSP-BF527
- USB 2.0 Interface to PC
- JTAG header footprint
- 32MB SDRAM
- 2 x Small Footprint 120 Pin Connectors
- Configurable Peripheral Interfaces - SPI - SPORT - I2C - GPIOs - Parallel - Timers

CN0216 evaluation software
Tedea-Huntleigh 505H-0002-F070 load cell or equivalent
Power supply: +6 V (EVAL-CFTL-6V-PWRZEVAL-CFTL-6V-PWRZ), or +6 V “wall wart”

Technical Documents

Learning Center

Type	Description
User Manual	ADI: User Manual for CN-0216 Precision Weigh Scale Design Using the AD7791 24-Bit Sigma-Delta ADC with External ADA4528-1 Zero-Drift Amplifiers
User Guide	ADI: User Guide for EVAL-SDP-CB1Z
Datasheet	ADI: Datasheet for AD7791 - Low Power, 24-Bit Sigma-Delta ADC Data Sheet (Rev 0)
Datasheet	ADI: Datasheet for ADA4528-1/ADA4528-2 - Precision, Ultralow Noise, RRIO, Zero-Drift Op Amp (Rev C)
Datasheet	ADI: Datasheet for ADP3301 - High Accuracy anyCAP 100 mA Low Dropout Linear Regulator Data Sheet (Rev 0)
Application Note	ADI: Application Note (AN-1114) for Lowest Noise Zero-Drift Amplifier Has 5.6 nV/√Hz Voltage Noise Density

Design Elements

Type	Description
Schematics	ADI: Schematics for EVAL-CN0216-SDPZ Evaluation Board
BOM	ADI: Bill of Material (BOM) for EVAL-CN0216-SDPZ Evaluation Board
Layout	ADI: Layout for EVAL-CN0216-SDPZ
Reference Design	ADI: Reference Design for CN0216 FMC-SDP Interposer and Evaluation Board / Xilinx KC705
Application Library	ADI: Application Library for BeMicro FPGA Project for CN0216 with Nios driver

Video

www.youtube.com/watch

Kit Features

Key Features for AD7791AD7791 are as below:

Power
- Supply: 2.5 V to 5.25 V operation
- Normal: 75 μA max
Power-down: 1 μA max
RMS noise: 1.1 μV at 9.5 Hz update rate
19.5-bit p-p resolution (22 bits effective resolution)
Integral nonlinearity: 3.5 ppm typical
Simultaneous 50 Hz and 60 Hz rejection
Internal clock oscillator
Rail-to-rail input buffer
VDD monitor channel

Key Features for ADA4528-1ADA4528-1 are as below:

Low offset voltage: 2.5 μV maximum
Low offset voltage drift: 0.015 μV/°C maximum
Low noise:
- 5.6 nV/√Hz at f = 1 kHz, AV = +100
- 97 nV p-p at f = 0.1 Hz to 10 Hz, AV = +100
Open-loop gain: 130 dB minimum
CMRR: 135 dB minimum
PSRR: 130 dB minimum
Unity-gain crossover: 4 MHz
Gain bandwidth product: 3 MHz at AV = 100
−3 dB closed-loop bandwidth: 6.2 MHz
Single-supply operation: 2.2 V to 5.5 V
Dual-supply operation: ±1.1 V to ±2.75 V
Rail-to-rail input and output
Unity-gain stable

Kit Contents

The Analog Devices EVAL-CN0216-SDPZEVAL-CN0216-SDPZ is supplied with below contents:

Evaluation Board

Tags: eval-cn0216-sdpz, adp3301, ad7791, ada4528-1, analog_devices