ANALOG DEVICES UG-078 Service Manual

Evaluation Board User Guide

UG-078

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

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

Low Power, Sigma-Delta ADC

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 ±V

REF

or ±V

/128. With the

REF

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.

PLEASE SEE THE LAST PAGE FOR AN IMPORTANT
WARNING AND LEGAL TERMS AND CONDITIONS.

FUNCTIONAL BLOCK DIAGRAM

AVDD

LOADCELL

CONNECTOR

ANALOG

INPUTS

Rev. 0 | Page 1 of 16

AD7780

VOLTAGE

REGULATOR

SPI/USB

INTERFACE

Figure 1.

USB

CONNECTOR

PC AND

LabVIEW™

BASED

SOFTWARE

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UG-078 Evaluation Board User Guide

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

REVISION HISTORY

2/10—Revision 0: Initial Version

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

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Evaluation Board User Guide UG-078

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.

Table 1. Evaluation Board Link Settings

Link Default Description

LK1, LK2 In

LK3, LK4 In

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

LK6 to LK11 In

LK12, LK13, LK14 In

LK15 10 Hz

LK16 128

These links are used to connect the AIN(+) and AIN(−) inputs to AV
analysis can be performed. With these links removed, an external voltage may be applied to AIN using the
SMB connectors.

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

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.

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.

These links are used for the bridge power-down switch. With LK12 inserted, the bridge power-down switch is
connected to AV
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 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 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.

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

DD

is used as the reference to the AD7780. REFIN(+) is connected to AVDD and

DD

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 Tab le 1.

/2. With this configuration, a noise

DD

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UG-078 Evaluation Board User Guide

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.

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+

REFIN−

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

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.

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.

SOCKETS

There are five sockets relevant to the operation of the AD7780
on this evaluation board. The functions of these sockets are
outlined in Tab l e 3.

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Evaluation Board User Guide UG-078

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 inter­face 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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