Evaluation Board for the AD7794 24-Bit, Low Power Sigma-Delta ADC (6 Channels)
EVAL-AD7794
processed by an on-chip digital filter. The analog input channel of the AD7794 accepts analog input signals of ±VREF/gain, with gain equal to 1 to 128. With a gain of 64 and the update rate programmed to 16.7 Hz, the rms noise is 87 nV. Simultaneous 50 Hz/60 Hz rejection is available at this data update rate also. Full data on the AD7794 is available in the AD7794 data sheet available from Analog Devices, Inc. and should be consulted in conjunction with this data sheet 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, which allows the user to easily communicate with the AD7794. Note that the AD7794 evaluation board software should be installed before connecting the AD7794 evaluation board to the PC.
Other components on the AD7794 evaluation board include the ADP3303 high precision, low power, 3.3 V output voltage regulator, which is used to power the USB/SPI interface.
FEATURES
Full-featured evaluation board for the AD7794 Standalone USB interface Various linking options
PC software for control of AD7794
GENERAL DESCRIPTION
This data sheet describes the evaluation board for the AD7794, which is a low power, 24-bit sigma-delta (Σ-Δ) ADC. The AD7794 is a complete analog front end for low frequency measurement applications. It contains six differential inputs and includes a low noise instrumentation amplifier, an embedded reference, programmable current sources, and a low side power switch. The update rate can be varied from 4.17 Hz to 470 Hz. It 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
FUNCTIONAL BLOCK DIAGRAM
AD7794VEXTERNALABCLK83.3VVOLTAGEREGULATOR07420-001USBCONNECTORSPI/USBINTERFACEPC ANDLabVIEW™-BASEDSOFTWARE5V Figure 1. Functional Block Diagram
Rev. 0
Evaluation boards are only intended for device evaluation and not for production purposes. Evaluation boards are supplied “as is” and without warranties of any kind, express, implied, or statutory including, but not limited to, any implied warranty of merchantability or fitness for a particular purpose. No license is granted by implication or otherwise under any patents or other intellectual property by application or use of evaluation boards. Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Analog Devices reserves the right to change devices or specifications at any time without notice. Trademarks and registered trademarks are the property of their respective owners. Evaluation boards are not authorized to be used in life support devices or systems.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
www.analog.com Tel: 781.329.4700
Fax: 781.461.3113 ©2008 Analog Devices, Inc. All rights reserved.
EVAL-AD7794
Installating the Software ...............................................................5 Using the Software ........................................................................5 Main Window ................................................................................6 Registers Window .........................................................................7 Other Registers Window ..............................................................8 Temp Demo Window ...................................................................9 Evaluation Board Schematic and Artwork .................................. 10 Ordering Information .................................................................... 13 Bill of Materials ........................................................................... 13 Ordering Guide .......................................................................... 13 ESD Caution................................................................................ 13
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 .......................................................................... 3 Sockets ........................................................................................... 3 Interfacing to the Evaluation Board ........................................... 4 Evaluation Board Software .............................................................. 5 Software Description.................................................................... 5
REVISION HISTORY
4/08—Revision 0: Initial Version
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SETUP CONDITIONS
Care should be taken before applying power and signals to the evaluation board to ensure that all link positions are set per the required operating mode. Table 2 shows the position in which all the links are initially set.
EVALUATION BOARD HARDWARE
POWER SUPPLIES
The AD7794 evaluation board is powered via the 5 V supply from the USB connector, J1. This 5 V supply can be used to power the AD7794 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 AD7794 can be powered using an external 3 V or 5 V power supply via J3.
SOCKETS
There are five sockets relevant to the operation of the AD7794 on this evaluation board. The functions of these sockets are outlined in Table 3.
LINKS
There are eight link options that must be set for the required operating setup before using the evaluation board. The
Lfunctions of these link options are outlined in Table 1.
L
Table 1. Evaluation Board Link Settings
Link Default Description
K1 In This link is used to externally short AIN1(+) to AIN1(−). If VBIAS is enabled and directed to AIN1(−) a noise analysis
in this configuration can be performed. With this link out, an external voltage can be applied to AIN1(+)/AIN(−) using the SMB connectors.
Out These links are used to connect the on-board temperature demonstration circuit to the ADC, and must all be in LLK2 to LK6
place when attempting to measure ambient temperature.
When the on-board temperature demonstration circuit is selected in software, LK6 allows current from the on chip current source of the AD7794 to flow through the temperature demonstration circuit. When LK4 and LK5 are in place, the 1 kΩ thermistor is connected to AIN4(+)/AIN4(−). When LK2 and LK3 are in place, the 5 kΩ precision resistor is used to generate the reference for the AD7794 so a ratiometric configuration of the temperature demonstration circuit is achieved.
K7 Out LK7 is used to test the on-chip low-side power switch. If LK7 is in place, enabling the low-side power switch
using PWR SW in the Registers window turns on the LED, D2. Clearing this bit turns off the LED.
K8 B LK8 is used to select the power source for AVDD on the AD7794. LK8 in Position A selects an external power
supply, supplied via J3. LK8 in Position B selects the 3.3 V regulated output from the on-board ADP3303 voltage regulator. LK8 in Position C selects the 5 V supply from the USB connector, J1.
Table 2. Initial Link and Switch Positions
Link No. LK1
LK2 to LK3 LK4 to LK5 LK6 LK7 LK8
Position In Out Out Out Out B
Function
AIN1(+) and AIN1(−) are shorted. Internal reference is used.
AIN4(+) and AIN4(−) are not connected to the temperature demonstration circuit. IOUT2 is not connected to temperature demonstration circuit.
LED D2 is not connected to the low-side power switch of the AD7794. The 3.3 V supply is used as AVDD for the AD7794.
Table 3. Socket Functions
Socket Description AIN1(+) Subminiature BNC (SMB) Connector. The analog input signal for the AIN1(+) input of the AD7794 is applied to this socket. AIN1(−) Subminiature BNC (SMB) Connector. The analog input signal for the AIN1(−) input of the AD7794 is applied to this socket. REFIN1(+) Subminiature BNC (SMB) Connector. This socket is used in conjunction with REFIN1− to apply an external reference to the
AD7794. The voltage for the REFIN1(+) input of the AD7794 is applied to this socket.
REFIN1(−) Subminiature BNC (SMB) Connector. This socket is used in conjunction with REFIN1+ to apply an external reference to the
AD7794. The voltage for the REFIN1(−) input of the AD7794 is applied to this socket.
J2 30-pin (2 × 15) Straight Header. This socket is used in conjunction with the prototype area to interface any signal to the AD7794.
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To set up the USB/SPI interface, use the following procedure: 1. Install the AD7794 evaluation board software using the
supplied AD7794 evaluation board CD before connecting the board to the PC.
2. After the AD7794 evaluation board software has been
installed, connect the board to the PC via J1 on the AD7794 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, select Continue Anyway to successfully complete the installation of the AD7794 evaluation board.
INTERFACING TO THE EVALUATION BOARD
Interfacing to the evaluation board is 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 AD7794 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 J3.
Communication between the AD7794 and the PC is via the USB/SPI interface. The on-board USB controller (U2) controls this communication.
07420-002
Figure 2. Hardware Installation Window
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drive. The installation program creates a program group called Analog Devices with a subgroup AD7794 in the Start menu of the taskbar.
5. Once the installation procedure is complete, double-click
on the AD7794 icon to start the program.
EVALUATION BOARD SOFTWARE
SOFTWARE DESCRIPTION
The AD7794 evaluation board is shipped with a CD containing software that can be installed onto a standard PC to control the AD7794. The software communicates with the AD7794 through the USB cable, which accompanies the board. The software allows you to configure the AD7794 and to read conversion data from the AD7794. Data can be read from the AD7794 and displayed or stored for later analysis. For further information, see the AD7794 data sheet available from Analog Devices.
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 on the main window. The Registers Window, Other Registers Window, and Temp Demo Window sections describe the most commonly used evaluation software windows.
The data that has been read can be exported to other packages such as MathCAD™ or Microsoft Excel for further analysis.
INSTALLATING 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\\AD7794 by default. 4. Once the directory is selected, the installation procedure
copies the files into the relevant directories on the hard
During power-up, the AD7794 evaluation board software confi-gures the device to have a gain of 64, the internal reference is selected, the AIN1(−)/AIN1(−) channel is selected, the bias voltage is enabled on AIN1(−), the update rate is set to 16.7 Hz and chop is enabled.
07420-004
Figure 3. AD7794 Evaluation Software Main Window
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Other Registers
This allows the user to access the ID register, status register, offset register, and full-scale register.
MAIN WINDOW
Menu Bar File
This 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.
Quick Analysis
This selects the Quick Analysis window. The Quick Analysis window gives the user access to the following subset of control bits: Channel, Update Rate, Gain, Reference Source, and Chop. For access to all control bits, click Registers or Other Registers.
About
This provides information on the revision of software used.
Buttons Reset
This allows the user to reset the AD7794 and set the registers to the power up conditions as specified by the software (channel = AIN1(−)/AIN1(−), bias voltage generator enabled on AIN1(−), gain = 64, update rate = 16.7 Hz, internal reference, chop enabled).
Temp Demo
This allows the user to access the temperature demonstration software.
Samples/Analysis
This serves the same purpose as the Sample button.
Waveform
The gathered conversions are displayed in graph form.
Exit
This allows the user to exit the software. It serves the same purpose as Quit in the File pull-down menu.
Histogram
The gathered samples are used to generate a histogram
Sample
This allows the user to read a number of samples from the AD7794. 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.
Codes
The gathered samples can be displayed in codes or in voltage format. When the Codes option is selected, the values are displayed as code. The Codes button changes to Volts. To display the information in volts, click Volts.
Continuous
This allows the user 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 then gathers the next group of samples.
Applied Reference
By default, the internal reference is used. To use an external reference, set Reference in the Registers window to REFIN1 if the external reference is applied between REFIN1(+) and REFIN1(−) or REFIN2 if the external reference is applied
between REFIN2(+) and REFIN2(−). The value of the external reference should be entered in the Applied Reference text box.
Registers
This allows the user to access the configuration register, mode register, and IO register.
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EVAL-AD7794
as the update rate, reference source, and the clock source. Consult the AD7794 data sheet for further details on the bit functions.
REGISTERS WINDOW
Click Registers to access the Registers window (see Figure 4). You can now access the configuration register, mode register, and IO register. This window allows you to change items such
07420-005
Figure 4. AD7794 Evaluation Software Registers Window
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calibration register. To write to the offset and full-scale
calibration registers, place the AD7794 is power-down or idle mode (using the Registers window).
OTHER REGISTERS WINDOW
Click Other Registers to access the Other Registers window (see Figure 5). This window displays the contents of the status register, ID register, offset calibration register, and full-scale
07420-006
Figure 5. AD7794 Evaluation Software Other Registers Window
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with a 210 μA excitation current; the AIN4(+)/AIN4(−) channel is selected as the analog input, the gain is set to 1, and the external reference REFIN1(+)/REFIN1(−) is selected. When you select Run, the software continuously reads the conversion from the AIN4(+)/AIN4(−)channel and converts the result to temperature using a look-up table.
When Run is clicked again, the temperature demonstration execution is halted. To exit the temperature demonstration, click the Back button. The software sets the configuration register, the mode register, and the I/O register to their pretemperature demonstration values.
TEMP DEMO WINDOW
Click Temp Demo to access the temperature demonstration window (see Figure 6). The AD7794 evaluation board has a temperature demonstration included on the board. To operate the temperature demonstration, LK2 to LK6 should be inserted and LK1 removed. With these links in place, the excitation current of the AD7794 is connected to a 1 kΩ thermistor which is connected across the AIN4(+)/AIN4(−) pins. In series with the thermistor is a 5 kΩ precision resistor, which is used to generate the reference voltage so that a ratiometric configura-tion is used. The temperature demonstration software saves the values in the mode register, configuration register, and IO register. The software then configures the AD7794 to operate
07420-007
Figure 6. AD7794 Evaluation Software Temperature Demo Window
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07420-010EVALUATION BOARD SCHEMATIC AND ARTWORK
Figure 7. AD7794 Evaluation Board Schematic
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07420-008
Figure 8. AD7794 Evaluation Board—Solder Side View
07420-009
Figure 9. AD7794 Evaluation Board—Component Side View
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07420-011
Figure 10. AD7794 Evaluation Board— Component Layout Diagram
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ORDERING INFORMATION
BILL OF MATERIALS
Table 4.
Qty Reference Designator Integrated Circuits 3 U1, U5, U6 1 U2 1 U3 L1 U4 1 Y1 2 D1, D2 1 L1 1 D3
Capacitors 19 C1 to C18, C44 1 C19 15 C20, C22, C27, C28, C32, C34 to C43 3 C21, C23, C26 2 C24, C25 1 C29 2 C30, C31 1 C33
Resistors 1 R1 1 R2 15 R3 to R16, R23 4 R17 to R20 2 R21, R22 4 R24 to R27 2 R28, R29 2 R30, R31 inks 8 LK1 to LK7 (2 × 1 way), LK8 (3 × 2 way) 8 At LK1 to LK8 Connectors 4 AIN1+, AIN1−, REFIN1+, REFIN1−, CLK 1 J1 1 J2 1 J3
Description
AD7794BRUZ USB controller 24LC64
ADP3303ARZ-3.3 24 MHz crystal Green LED Ferrite bead Diode Capacitors 100 pF ceramic
0.1 μF ± 10% ceramic 10 μF tantalum 1 μF ceramic 2.2 μF tantalum 22 pF ceramic 47 μF tantalum
1 kΩ thermistor 5 kΩ ± 0.1% 0 Ω resistor 1 MΩ resistor 100 kΩ resistor 10 kΩ resistor 2.2 kΩ resistor 1 kΩ resistor Pin headers Shorting plugs
SMB connector
USB Mini-B connector 30-pin (2 × 15) header 2-way terminal block
Manufacturer/Part No.
Analog Devices
Cypress Semiconductor Corporation, CY7C68013A-56LFXC Microchip Technology Inc., 24LC64-I/SN Analog Devices
AEL Crystals, X24M000000S244
Fairchild Semiconductor, QTLP630C-4 Meggitt Sigma, BMB2A0300AN1
Micro Commercial Components Corp., DL4001-TP Not inserted
AVX Corporation, 06035A101JAT2A AVX Corporation, CM105X7R104K16AT AVX Corporation, TAJA106K010R Yageo Corporation, 2238 246 19863 EPCOS AG, B45196E2225K109
Yageo Corporation, 2238 867 15229 AVX Corporation, TAJC476K016R
EPCOS AG, B57620C102J62
Tyco Electronics Corporation, RN73C2A4K99BTG Multicomp, MC 0.063W 0603 0R Multicomp, MC 0.063W 0603 1% 1M Multicomp, MC 0.063W 0603 1% 100K Multicomp, MC 0.063W 0603 1% 10K Multicomp, MC 0.063W 0603 1% 2K2 Multicomp, MC 0.063W 0603 1% 1K
Harwin Plc, M20-9983646 Harwin Plc, M7566-05 Not inserted
Molex, 565790576
Harwin Plc, M20-9983646
Camden Electronics Ltd., CTB5000/2
ORDERING GUIDE
Model Description EVAL-AD7794EBZ1Evaluation Board
ESD CAUTION
1
Z = RoHS Compliant Part.
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NOTES
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NOTES
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NOTES
©2008 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners. EB07420-0-4/08(0)
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