AD7721_EvalBoard| Application Note
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FEATURES
Evaluation Board for Single Supply, 12/16-Bit 312.5/468.75 kHz - ADC EVAL-AD7721CB
AD7721 EVALUATION BOARD FEATURES
Full-Featured Evaluation Board for the AD7721 EVAL-CONTROL BOARD Compatible Stand Alone Capability On-board Analog Filtering and Reference Various Linking Options PC Software for Control and Data Analysis when used with EVAL-CONTROL BOARD INTRODUCTION
On-board components include an AD780 precision bandgap voltage reference and opamps to condition the analog input and configure it to drive the AD7721 with single-ended or complimentary input signals.
Power Supplies
When using this evaluation board with the Eval-Control Board all supplies are provided from the Eval-Control Board through the 96-way connector. When using the board as a stand alone unit external supplies must be provided. This evaluation board has four analog power supply inputs: AVDD, AGND, VDD and VSS. AVDD is used to provide 5 V for the AD7721 and VIN for the AD780 voltage reference. The VDD and VSS power supplies are used to power the operational amplifiers which form the anti-alias filters. These power supplies can be applied externally by the user or they can be obtained from the Eval-Control board via the 96-way edge connector. The supplies available from the Eval-Control board are +5 V to power the AD7721 and reference and +12 V/-12 V to drive the operational amplifiers. DGND and DVDD connections are also available. The DVDD is used to provide the DVDD for the AD7721. DGND and AGND are connected at the AD7721 so it is not recommended to connect them else where in the system. All power supplies are
decoupled to ground. The power supplies are decoupled using 22uF tantalum capacitors in parallel with 10nF ceramic capacitors.
This Technical Note describes the evaluation board for the AD7721. The AD7721 is a complete, low power, 12/16-bit, sigma-delta ADC which operates from a 5V power supply. The device consists of a modulator and 2 FIR filters which filter and decimate the modulator output. Its versatile interface structure allows both serial and parallel connection to a microprocessor, the device connecting directly to Analog Devices, Motorola and Texas Instruments DSPs. Full data on the AD7721 is available in the AD7721 data sheet available from Analog Devices. The data sheet should be consulted in conjunction with this Technical Note when using the Evaluation Board.
OPERATING THE AD7721 EVALUATION BOARD
The EVAL-AD7721CB can be used as a stand-alone unit or with the EVAL-ControlBoard which is available from Analog Devices under the order entry "EVAL-CONTROL BRD2". A 96-way DIN connector (J3) interfaces the EVALAD7721CB directly to the Eval-Control Board. Software is provided with the evaluation board package to allow analysis of the ADCs performance when using the Eval-Control board.
FUNCTIONAL BLOCK DIAGRAM
AVDD
AGND
DVDD
DGND
VDD
VSS
EXT CLK AD7721 ADC 96-WAY CONNECTOR
VIN
BIASING CIRCUIT
ANTI-ALIAS FILTER
BIASING CIRCUIT
ANTI-ALIAS FILTER
AD780 REFERENCE
REV. A
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 which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. One Technology Way, P.O. Box 9106, Norwood. MA 02062-9106, U.S.A. Tel: 617/329-4700 World Wide Web Site: http://www.analog.com Fax: 617/326-8703 c Analog Devices, Inc., 2002
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