Analog Devices: CN0251 Reference Design for A Flexible 4-Channel Analog Front End for Wide Dynamic Range Signal Conditioning

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Kit Overview

The EVAL-CN0251-SDPZEVAL-CN0251-SDPZ circuit is a flexible signal conditioning circuit for processing signals of wide dynamic range, varying from several mV p-p to 20 V p-p. The circuit provides the necessary conditioning and level shifting and achieves the dynamic range using the internal programmable gain amplifier (PGA) of the high resolution analog-to-digital converter (ADC).

The EVAL-CN0251-SDPZEVAL-CN0251-SDPZ circuit provides programmable gain, high CMR, and high input impedance. The input signal passes through the 4-channel ADG1409 multiplexer into the AD8226AD8226 low cost, wide input range instrumentation amplifier. The AD8226 offers high CMR up to 80 dB and very high input impedance (800 MΩ differential mode and 400 MΩ common mode). A wide input range and rail-to-rail output allow the AD8226 to make full use of the supply rails.

The AD8475 is a fully differential, attenuating amplifier with integrated precision gain resistors. It provides precision attenuation (G = 0.4 or G = 0.8), common-mode level shifting, and single-ended-to-differential conversion. The AD8475 is an easy to use, fully integrated precision gain block, designed to process signal levels up to ±10 V on a single supply. Therefore, the AD8475 is suitable for attenuating signals from the AD8226 up to 20 V p-p, while maintaining high CMR and offering a differential output to drive the differential input ADC.

The AD7192 is a 24-bit sigma-delta (Σ-Δ) ADC with an internal PGA. The on-chip, low noise gain stage (G = 1, 8, 16, 32, 64, or 128) means that signals of large and small amplitude can be interfaced directly to the ADC.

The circuit test setup uses the EVAL-CN0251-SDPZEVAL-CN0251-SDPZ circuit evaluation board and the System Demonstration Platform (SDP-B) evaluation board (EVAL-SDP-CB1ZEVAL-SDP-CB1Z) should be purchased seperately. The two boards have 120-pin mating connectors, allowing for the quick setup and evaluation of the performance of the circuit. The EVAL-CN0251-SDPZ board contains the circuit to be evaluated and the SDP is used with the CN-0251 evaluation software to capture the data from the EVAL-CN0251-SDPZ. The SDP is also used to control the input multiplexer and various functions within the AD7792BRUZ.AD7792BRUZ. ADC.

Key Applications: Programmable Logic Controllers/ Distributed Control Systems

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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-CN0251-SDPZEVAL-CN0251-SDPZ circuit evaluation board
EVAL-SDP-CB1ZEVAL-SDP-CB1Z controller 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

CN0241 SDP evaluation software
A dc supply: +15 V, -15 V, and +6 V

Technical Documents

Learning Center

Type	Description
User Manual	ADI: User Manual for CN-0251 A Flexible 4-Channel Analog Front End for Wide Dynamic Range Signal Conditioning
User Guide	ADI: User Guide for EVAL-SDP-CB1Z
User Guide	ADI: Getting Started with SDP
Datasheet	ADI: Datasheet for AD8475: Precision, Selectable Gain, Fully Differential Funnel Amplifier (Rev B)
Datasheet	ADI: Datasheet for ADG1408/ADG1409: 4ohm Ron, 4-/8-Channel 15 V/+12 V/5 V iCMOS Multiplexers (Rev B)
Datasheet	ADI: Datasheet for AD7192: 4.8 kHz Ultra-Low Noise 24-Bit Sigma-Delta ADC with PGA (Rev A)
Datasheet	ADI: Datasheet for ADP1720: 50 mA, High Voltage, Micropower Linear Regulator (Rev A)
Datasheet	ADI: Datasheet for AD8226: Wide Supply Range, Rail-to-Rail Output Instrumentation Amplifier (Rev C)
Datasheet	ADI: Datasheet for ADR440/ADR441/ADR443/ADR444/ADR445: Ultralow Noise, LDO XFET Voltage References with Current Sink and Source (Rev E)

Design Elements

Type	Description
Schematics	ADI: Schematics for EVAL-CN0251-SDPZ Evaluation Board
Layout	ADI: Layout for EVAL-CN0251-SDPZ
BOM	ADI: Bill Of Material (BOM) for EVAL-CN0251-SDPZ Evaluation Board

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Kit Features

Devices Used for the EVAL-CN0251-SDPZEVAL-CN0251-SDPZ Evaluation Board
Key Features for ADG1409: 4.7 Ω maximum on resistance @ 25°C 0.5 Ω on resistance flatness Up to 190 mA continuous current Fully Specified at ±15 V /12 V /±5 V 3 V Logic Compatible Inputs Rail - to - Rail Operation Break - Before - Make Switching Action 16 - Lead TSSOP Packages and 4 mm × 4 mm LFCSP packages Typical Power Consumption (< 0.03 µW)	Key Features for AD8226: Gain set with 1 external resistor Gain range: 1 to 1000 Input voltage goes below ground Inputs protected beyond supplies Very wide power supply range Single supply: 2.2 V to 36 V Dual supplies: ±1.35 V to ±18 V Bandwidth (G = 1): 1.5 MHz CMRR (G = 1): 90 dB minimum for BR models Input noise: 22 nV/√Hz Typical supply current: 350 μA

Key features for AD8475: Attenuate and level shift Attenuation: G = 0.4x, 0.8x Fully differential or single-ended input/output Differential output designed to drive precision ADCs Drives switched capacitor and Σ-Δ ADCs Rail-to-rail output VOCM pin adjusts output common mode Robust over-voltage protection up to ±15V (VS = +5 V) Single supply: 3V to 10V Dual supplies: ±1.5V to ±5V High performance Suited for driving 18-bit converter up to 4 MSPS 10 nV/√Hz output noise 3 ppm/°C gain drift	Key Features for AD7192: RMS noise: 11 nV @ 4.7 Hz (gain = 128) 15.5 noise-free bits @ 2.4 kHz (gain = 128) Up to 22 noise-free bits (gain = 1) Offset drift: 5 nV/°C Gain drift: 1 ppm/°C Specified drift over time 2 differential/4 pseudo differential input channels Automatic channel sequencer Programmable gain (1 to 128)

Key Features for ADP1720: Wide input voltage range: 4 V to 28 V Maximum output current: 50 mA Low light load current: 28 μA at 0 μA load, 35 μA at 100 μA load Low shutdown current: 0.7 μA Low dropout voltage: 275 mV @ 50 mA load Initial accuracy: ±0.5% Accuracy over line, load, and temperature: ±2% Stable with small 1μF ceramic output capacitor Fixed 3.3 V and 5.0 V output voltage options Adjustable output voltage option: 1.225 V to 5.0 V Current limit and thermal overload protection Logic controlled enable Download ADP1720-EP Data Sheet (pdf) Enhanced processing (EP) for −55°C to +125°C operation	Key Features for ADR444: Ultralow noise (0.1 Hz to 10 Hz) ADR440: 1 μV p-p ADR441: 1.2 μV p-p ADR443: 1.4 μV p-p ADR444: 1.8 μV p-p ADR445: 2.25 μV p-p Input range: (VOUT + 500 mV) to 18 V Superb temperature coefficient A Grade: 10 ppm/°C B Grade: 3 ppm/°C Low dropout operation: 500 mV High output source and sink current +10 mA and −5 mA, respectively

Devices Used for the EVAL-CN0251-SDPZEVAL-CN0251-SDPZ Evaluation Board

Key Features for ADG1409:

4.7 Ω maximum on resistance @ 25°C
0.5 Ω on resistance flatness
Up to 190 mA continuous current
Fully Specified at ±15 V /12 V /±5 V
3 V Logic Compatible Inputs
Rail - to - Rail Operation
Break - Before - Make Switching Action
16 - Lead TSSOP Packages and 4 mm × 4 mm LFCSP packages
Typical Power Consumption (< 0.03 µW)

Key Features for AD8226:

Gain set with 1 external resistor
Gain range: 1 to 1000
Input voltage goes below ground
Inputs protected beyond supplies
Very wide power supply range
- Single supply: 2.2 V to 36 V
- Dual supplies: ±1.35 V to ±18 V
Bandwidth (G = 1): 1.5 MHz
CMRR (G = 1): 90 dB minimum for BR models
Input noise: 22 nV/√Hz
Typical supply current: 350 μA

Key features for AD8475:

Attenuate and level shift
Attenuation: G = 0.4x, 0.8x
Fully differential or single-ended input/output
Differential output designed to drive precision ADCs
Drives switched capacitor and Σ-Δ ADCs
Rail-to-rail output
VOCM pin adjusts output common mode
Robust over-voltage protection up to ±15V (VS = +5 V)
Single supply: 3V to 10V
Dual supplies: ±1.5V to ±5V
High performance
Suited for driving 18-bit converter up to 4 MSPS
10 nV/√Hz output noise
3 ppm/°C gain drift

Key Features for AD7192:

RMS noise: 11 nV @ 4.7 Hz (gain = 128)
15.5 noise-free bits @ 2.4 kHz (gain = 128)
Up to 22 noise-free bits (gain = 1)
Offset drift: 5 nV/°C
Gain drift: 1 ppm/°C
Specified drift over time
2 differential/4 pseudo differential input channels
Automatic channel sequencer
Programmable gain (1 to 128)

Key Features for ADP1720:

Wide input voltage range: 4 V to 28 V
Maximum output current: 50 mA
Low light load current: 28 μA at 0 μA load, 35 μA at 100 μA load
Low shutdown current: 0.7 μA
Low dropout voltage: 275 mV @ 50 mA load
Initial accuracy: ±0.5%
Accuracy over line, load, and temperature: ±2%
Stable with small 1μF ceramic output capacitor
Fixed 3.3 V and 5.0 V output voltage options
Adjustable output voltage option: 1.225 V to 5.0 V
Current limit and thermal overload protection
Logic controlled enable
Download ADP1720-EP Data Sheet (pdf)
Enhanced processing (EP) for −55°C to +125°C operation

Key Features for ADR444:

Ultralow noise (0.1 Hz to 10 Hz)
- ADR440: 1 μV p-p
- ADR441: 1.2 μV p-p
- ADR443: 1.4 μV p-p
- ADR444: 1.8 μV p-p
- ADR445: 2.25 μV p-p
Input range: (VOUT + 500 mV) to 18 V
Superb temperature coefficient
- A Grade: 10 ppm/°C
- B Grade: 3 ppm/°C
Low dropout operation: 500 mV
High output source and sink current
+10 mA and −5 mA, respectively

Kit Contents

The Analog Devices EVAL-CN0251-SDPZEVAL-CN0251-SDPZ kit is supplied with below contents:

Evaluation Board