This version (26 May 2023 09:25) was approved by Trisha Cabildo.
Table of Contents
EVAL-AD7690-PMDZ PulSAR ADC PMOD User Guide
The EVAL-AD7690-PMDZ offers a very high performance of 18 bits with a throughput of 400 kSPS in a PMOD form factor. It is designed to demonstrate the performance of AD7690 and to provide an easy digital interface for a variety of system applications.
The AD7690 is an 18-bit, successive approximation, analog to digital converter (ADC) that operates from a single power supply, VDD. It contains a low-power, high-speed, 18-bit sampling ADC with no missing codes, an internal conversion clock, and a versatile serial interface port.
* The throughput of your PulSAR ADC will be limited to the SPI bus speed of your platform.
Hardware Setup
The PMOD board is small in size with dimensions approximately 1 inch in width by 3 inches in length.
Power Supply Requirements
Typically, when using a PMOD board the power for the module comes directly from the host board it is connected to. The power is generally capable of providing up to 100 mA at 3.3V, and for complete power specifications please click here.
In the case of the high precision, successive approximation ADC's architecture, it was required to provide low noise external power supplies to obtain datasheet results. The AD7690 ADC is driven by precision amplifiers which are also optimized for noise and power. In order to enable those amplifiers to provide zero and full-scale inputs to the ADC, power supplies above and below the ADC input range were needed.
With all these factors combined, the board was designed using external power supplies of -2.5V, GND, and 7.5V. These supplies provide the power for the entire PMOD board, so even though power is coming in through the PMOD connector, it's not actually powering the components on the board.
Input Connectors
For the input signals coming into the EVAL-AD7690-PMDZ, SMB connectors were chosen to help minimize the noise at the input. There are two (2) SMB connectors per board, and that's because there are both positive(+) and negative(-) inputs to each converter. This will provide the user with the cleanest input signal possible, and fully utilize the resolution and speed of the converters.
Each of the converters also has a combination of single-ended inputs, differential inputs, or pseudo-differential inputs. So in order to determine the input style of your converter it is imperative to look at the datasheet of the device you are using. The datasheet of any device should always be followed before using it in an application or on a board.
Digital Interface (PMOD)
The PMOD interface is a series of standardized digital interfaces for various digital communication protocols such as SPI, I2C, and UART. These interface types were standardized by Digilent, which is now a division of National Instruments. Complete details on the PMOD specification can be found here.
The specific interface used for the PulSAR PMOD boards is the extended SPI. In general, ADI has adopted the extended SPI connector for all PMOD devices which have an SPI interface. It provides flexibility to add interrupts, general purpose I/O, resets, and other important digitally controlled functions.
Above is the connection of the EVAL-AD7690-PMDZ to the SPI PMOD connector. It is hardware configured in a 3-wire mode with no busy indicator. This basically means that the only signals that go between the converter and the processor are the CNV (similar to a chip select in this mode), SCLK (serial Clock), and MISO (serial data out). There are no registers internal to the AD7690 ADC, so there is no need for a data input line, the data just streams out using the CNVST pin.
More information and Useful links
Schematics, PCB Layout, Bill of Materials
Additional Information
Registration
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resources/eval/user-guides/circuits-from-the-lab/eval-ad7690-pmdz.txt · Last modified: 18 May 2023 12:21 by Trisha Cabildo