Analog Devices AD7780 Manual de usuario

Evaluation Board User Guide

UG-078

One Technology Way •P. O. Box 9106 •Norwood, MA 02062-9106, U.S.A. •Tel: 781.329.4700 •Fax: 781.461.3113 •www.analog.com

Evaluation Board for the AD7780 24-Bit, Pin-Programmable,

Low Power, Sigma-Delta ADC

PLEASE SEE THE LAST PAGE FOR AN IMPORTANT

WARNING AND LEGAL TERMS AND CONDITIONS. Rev. 0 | Page 1 of 16

FEATURES

Full-featured evaluation board for the AD7780

Standalone USB interface

Various linking options

PC software for control of AD7780

GENERAL DESCRIPTION

This user guide describes the evaluation board for the AD7780

which is a pin-programmable, low power, 24-bit sigma-delta

(Σ-Δ) ADC. The AD7780 is a complete analog front end for

low frequency measurement applications such as bridge sensor

systems. It contains one differential input and includes a low

noise instrumentation amplifier. The output data rate can be

programmed to 10 Hz or 16.7 Hz. The AD7780 also has an

on-board clock, eliminating the need for an external clock. It

employs a Σ-Δ conversion technique to realize up to 24 bits of

no missing codes performance. The input signal is applied to

an analog modulator. The modulator output is processed by an

on-chip digital filter. The analog input channel of the AD7780

accepts analog input signals of ±VREF or ±VREF/128. With the

update rate programmed to 10 Hz, the rms noise is 44 nV when

the gain is 128. Simultaneous 50 Hz/60 Hz rejection is available

at both output data rates.

Full data on the AD7780 is available in the AD7780 data sheet

available from Analog Devices, Inc., and should be consulted in

conjunction with this user guide when using the evaluation board.

The evaluation board interfaces to the USB port of an IBM®-

compatible PC. Software is available with the evaluation board

that allows users to easily communicate with the AD7780.

Note that the AD7780 evaluation board software should be

installed before connecting the AD7780 evaluation board

to the PC.

Another component on the AD7780 evaluation board is the

ADP3303 high precision, low power, 3.3 V output voltage

regulator, which is used to power the USB/SPI interface.

FUNCTIONAL BLOCK DIAGRAM

AD7780

ANALOG

INPUTS

VOLTAGE

REGULATOR

SPI/USB

INTERFACE

USB

CONNECTOR PC AND

LabVIEW™

BASED

SOFTWARE

AVDD

LOADCELL

CONNECTOR

08748-001

Figure 1.

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UG-078 Evaluation Board User Guide

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TABLE OF CONTENTS

Features .............................................................................................. 1

General Description......................................................................... 1

Functional Block Diagram .............................................................. 1

Revision History ............................................................................... 2

Evaluation Board Hardware............................................................ 3

Power Supplies .............................................................................. 3

Links............................................................................................... 3

Setup Conditions .......................................................................... 4

Sockets ........................................................................................... 4

Interfacing to the Evaluation Board........................................... 5

Evaluation Board Software...............................................................6

Software Description ....................................................................6

Installing the Software..................................................................6

Using the Software ........................................................................6

Main Window ................................................................................7

Weighscale Demo Window..........................................................8

Evaluation Board Schematic and Artwork.....................................9

Ordering Information.................................................................... 13

Bill of Materials........................................................................... 13

REVISION HISTORY

2/10—Revision 0: Initial Version

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Evaluation Board User Guide UG-078

Rev. 0 | Page 3 of 16

EVALUATION BOARD HARDWARE

POWER SUPPLIES

The AD7780 evaluation board is powered via the 5 V supply

from the USB connector, J1. This 5 V supply can be used to

power the AD7780 directly. A 3.3 V regulated voltage from the

on-board ADP3303 (a high precision, low power, 3.3 V output

voltage regulator) can also be used. Alternatively, the AD7780 can

be powered using an external 3 V or 5 V power supply via J2.

LINKS

There are sixteen groups of link options that must be set for the

required operating setup before using the evaluation board. The

functions of these link options are outlined in Table 1 .

Table 1. Evaluation Board Link Settings

Link Default Description

LK1, LK2 In These links are used to connect the AIN(+) and AIN(−) inputs to AVDD/2. With this configuration, a noise

analysis can be performed. With these links removed, an external voltage may be applied to AIN using the

SMB connectors.

LK3, LK4 In With LK3 and LK4 in place, AVDD is used as the reference to the AD7780. REFIN(+) is connected to AVDD and

REFIN(−) is connected to GND. To use another reference source, remove LK3 and LK4.

LK5 3.3 V LK5 is used to select the power source for AVDD on the AD7780.

In Position A, LK5 selects an external power supply, supplied via J2.

In Position B, LK5 selects the 3.3 V regulated output from the on-board ADP3303 voltage regulator.

In Position C, LK5 selects the 5 V supply from the USB connector, J1.

LK6 to LK11 In These links connect the serial interface pins of the AD7780 to the SPI interface of the microcontroller. The

links should be in place to use the AD7780 evaluation board software. With these links removed, the AD7780

can be interfaced to an external microcontroller.

LK12, LK13, LK14 In These links are used for the bridge power-down switch. With LK12 inserted, the bridge power-down switch is

connected to AVDD through an LED. When the bridge power-down switch is closed, the LED turns on. LK13

should be open when LK12 is inserted.

LK13 and LK14 are used when a load cell is connected to Header J4. LK12 should be left open. With LK13

inserted, the bridge power-down switch is connected to Header J4. The low side of the load cell can be

connected to GND through the bridge power-down switch. With LK14 inserted, the low side of the load cell is

connected directly to GND. The REFIN(−) terminal should be shorted to the GND/PSW terminal on Header J4

to enable the previous functions.

LK15 10 Hz

LK15 is used to select the output data rate for the AD7780. With LK15 in Position 10 Hz, the output data rate is

set to 10 Hz. When LK15 is in Position 16.7 Hz, the output data rate is set to 16.7 Hz.

LK16 128

LK16 is used to select the gain of the AD7780. With LK16 in Position 1, the gain is set to 1. With LK16 in

Position 128, the gain of the AD7780 is set to 128.

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UG-078 Evaluation Board User Guide

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SETUP CONDITIONS

Take care before applying power and signals to the evaluation

board to ensure that all link positions are set per the required

operating mode. Tabl e 2 shows the position in which all the

links are initially set.

SOCKETS

There are five sockets relevant to the operation of the AD7780

on this evaluation board. The functions of these sockets are

outlined in Table 3.

Table 2. Initial Links and Positions

Link No. Position Function

LK1, LK2 In AIN(+) and AIN(−) are shorted to AVDD/2.

LK3, LK4 In The reference voltage is set to 3.3 V (AVDD).

LK5 B The 3.3 V supply is used as AVDD for the AD7780.

LK6 to LK11 In The AD7780 is interfaced to the on-board microcontroller.

LK12 In The bridge power-down switch is connected to AVDD.

LK13 Out The bridge power-down switch is disconnected from Header J4.

LK14 In Terminal GND/PSW of Header J4 is connected to GND.

Table 3. Socket Functions

Socket Description

AIN+ Subminiature BNC (SMB) connector. The analog input signal for the AIN(+) input of the AD7780 is applied to this socket.

AIN− Subminiature BNC (SMB) connector. The analog input signal for the AIN(−) input of the AD7780 is applied to this socket.

REFIN+ Subminiature BNC (SMB) connector. This socket is used in conjunction with REFIN− to apply an external reference to the AD7780.

The voltage for the REFIN(+) input of the AD7780 is applied to this socket.

REFIN− Subminiature BNC (SMB) connector. This socket is used in conjunction with REFIN+ to apply an external reference to the AD7780.

The voltage for the REFIN(−) input of the AD7780 is applied to this socket.

J4 6-pin terminal block. This is used to connect an external load cell to the AD7780 evaluation board.

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Evaluation Board User Guide UG-078

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INTERFACING TO THE EVALUATION BOARD

Interface to the evaluation board via a standard USB connector,

J1. J1 is used to connect the evaluation board to the USB port

of a PC. A standard USB connector cable is included with the

AD7780 evaluation board to allow the evaluation board to inter-

face with the USB port of the PC. Because the board is powered

via the USB connector, there is no need for an external power

supply, although if preferred, one may be connected via J2.

Communicate between the AD7780 and the PC via the

USB/SPI interface. The on-board USB controller (U2)

handles this communication.

To set up the USB/SPI interface, use the following procedure:

1. Install the AD7780 evaluation board software using the

supplied AD7780 evaluation board CD before connecting

the board to the PC.

2. After the AD7780 evaluation board software is installed,

connect the board to the PC via J1 on the AD7780 evaluation

board and via the USB port on the PC using the supplied

USB connector cable. The PC automatically finds the new

USB device and identifies it as the AD779x Evaluation Board.

3. Follow the on-screen instructions that appear. During the

installation process, if the Hardware Installation Wizard

appears as shown in Figure 2, click Continue Anyway to

complete the installation of the AD7780 evaluation board.

8748-002

Figure 2. Hardware Installation Window

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UG-078 Evaluation Board User Guide

Rev. 0 | Page 6 of 16

EVALUATION BOARD SOFTWARE

SOFTWARE DESCRIPTION

The AD7780 evaluation board is shipped with a CD containing

software that can be installed onto a standard PC to control the

AD7780. The software communicates with the AD7780 through

the USB cable, which accompanies the board. The software allows

you to read conversion data from the AD7780. Data can be read

from the AD7780 and displayed or stored for later analysis. For

further information, see the AD7780 data sheet available from

Analog Devices.

INSTALLING THE SOFTWARE

Use the following steps to install the software:

1. Start Windows® and insert the CD.

2. The installation software should launch automatically. If it

does not, use Windows Explorer to locate the setup.exe file

on the CD. Double-click this file to start the installation

procedure.

3. At the prompt, select a destination directory, which is

C:\Program Files\Analog Devices\AD7780 by default.

Once the directory is selected, the installation procedure

copies the files into the relevant directories on the hard

drive. The installation program creates a program group

called Analog Devices with the subgroup AD7780 in the

Start menu of the taskbar.

4. Once the installation procedure is complete, double-click

on the AD7780 icon to start the program.

USING THE SOFTWARE

Figure 3 shows the main window that is displayed when the

program starts. The Main Window section briefly describes

the various menu and button options in the main window.

The data that has been read can be exported to other packages,

such as MathCAD™ or Microsoft® Excel, for further analysis.

08748-003

Figure 3. AD7780 Evaluation Software Main Window

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Evaluation Board User Guide UG-078

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MAIN WINDOW

Menu Bar

File

The File menu allows the user to read previously stored data for

display or analysis, write the current set of data to a file for later

use, and exit the program.

About

The About menu provides information on the revision of

software used.

Buttons

Reset

This button allows you to reset the AD7780 software.

Exit

This button allows you to exit the software. It serves the same

purpose as Quit in the File pull-down menu.

Sample

This button allows you to read a number of samples from the

AD7780. Noise analysis is then performed on the samples.

These samples can be stored for further analysis. The sample

size is entered in the Num Samples text box.

Continuous

This button allows you to read a number of samples

continuously. The software gathers a number of samples

as specified by the Num Samples text box, performs noise

analysis on the samples, and gathers the next group of samples.

Weighs c ale Demo

This button allows you to access the weighscale demonstration

software.

Output Data Rate

This text box displays the output data rate of the AD7780.

Gain

This text box displays the gain of the AD7780.

Status Bits

This text box displays the status bits of the AD7780.

Waveform

The gathered conversions are displayed in graph form.

Histogram

The gathered samples are used to generate a histogram.

Codes

The gathered samples can be displayed in codes or in voltage

format. When the Codes button is selected, the values are

displayed as code. The Codes button changes to Volts. To

display the information in volts, click Volts.

Reference

Enter the value of the external reference in the Reference (V)

text box.

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UG-078 Evaluation Board User Guide

Rev. 0 | Page 8 of 16

WEIGHSCALE DEMO WINDOW

Click Weighsc ale Demo (in the main window) to access

the weighscale demo window (see Figure 4). The AD7780

evaluation board has a header, J3/J4, which allows you to

interface the ADC to a load cell. To connect a load cell to the

AD7780 evaluation board, LK1, LK2, LK3 and LK4 must be

removed. A 6-wire load cell can be connected to Header J3/J4.

With the load cell connected to the evaluation board, click the

RUN button (the button changes to a STOP button after being

clicked). The software then begins reading conversions from

the AD7780. The output data rate and gain are continuously

monitored so you can change either the gain or output data

rate within the weighscale demo window. The output data rate

and gain being used by the AD7780 are reflected in the Output

Data Rate and Gain text boxes. The maximum weight being

applied to the loadcell must be entered in the Full-Scale Weight

(Kg) text box. The Zero-Scale Calibration button performs an

offset calibration, which is useful to remove the TARE of the

load cell. With the full-scale weight placed on the load cell, a

full-scale calibration is performed by clicking the Full-Scale

Calibration button.

To stop conversions, click the STOP button. To exit the

Weighscale Demo, click the BACK button.

08748-004

Figure 4. AD7780 Evaluation Software Weighscale Demo Window

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Evaluation Board User Guide UG-078

Rev. 0 | Page 9 of 16

EVALUATION BOARD SCHEMATIC AND ARTWORK

08748-005

Figure 5. AD7780 Evaluation Board Schematic

UG-078 Evaluation Board User Guide

Rev. 0 | Page 10 of 16

08748-006

Figure 6. AD7780 Evaluation Board—Solder Side View

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