AD7940 STAMP SPI DAUGHTER CARD

Description

The AD7940 STAMP SPI Daughter Card is a compact AD7940 (14-bit 100 kSPS Low Power ADC) evaluation board which can be used in conjunction with the uClinux STAMP board (BF533-STAMP). The part number for this evaluation board is AD7940-DBRD.

AD7940

Connection to the uClinux Stamp Board

The Daughter Card can be connected through its 20-pin connector to the Stamp board. This connection should be made so that the BNC connector juts out over the edge of the Stamp Board. This connection means that the SPI interface (CS,SCLK and SDATA) and power signals being created by the Stamp board are applied to the AD7940 device through the Daughter Card.

The Stamp board supplies a 7.5 V dc power signal to the Daughter Card. The 7.5 V dc signal is used to create the voltage reference for the AD7940 by providing the input to the ADP3300 (IC1) Low Dropout linear regulator which produces the 5 V input to the REF198 (IC2) reference. The REF198 outputs the 4.096 V reference (Vref) used by the AD7940. The AD7940 full-scale voltage is 0-Vref.

Analog Input, VIN

The analog input (VIN) is attached through the BNC connector on the Daughter Card. The maximum peak to peak value of this input is VREF. VIN is buffered and then passes through a 2 MHz anti-alias filter (1st order passive low-pass filter) before being input to the AD7940.

Operation for AC and DC analog input voltages

The link positions for the jumpers (JP1 and JP2) needed for operating the Daughter Card for AC and DC input voltages are detailed on the bottom right hand corner of the Daughter Card under the BNC connector.

DC input voltages:
The two pins of JP1 which are furthest away the BNC connector must be connected. JP2 is left open.

AC input voltages:
The two pins of both JP1 and JP2 which are nearest the BNC connector must be connected.

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