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AD5160 Pmod Xilinx FPGA Reference Design

Introduction

The AD5160 provides a compact 2.9 mm × 3 mm packaged solution for 256-position adjustment applications. These devices perform the same electronic adjustment function as mechanical potentiometers1 or variable resistors but with enhanced resolution, solid-state reliability, and superior low temperature coefficient performance. The wiper settings are controllable through an SPI-compatible digital interface. The resistance between the wiper and either end point of the fixed resistor varies linearly with respect to the digital code transferred into the RDAC latch. Operating from a 2.7 V to 5.5 V power supply and consuming less than 5 μA allows for usage in portable battery-operated applications.

HW Platform(s):

System: Microblaze, AXI, UART

Quick Start Guide

The bit file provided in the project *.zip file combines the FPGA bit file and the SDK elf files. It may be used for a quick check on the system. All you need is the hardware and a PC running a UART terminal and the programmer (IMPACT).

Required Hardware

Required Software

Xilinx ISE 13.2 (Programmer (IMPACT) is sufficient for the demo and is available on Webpack).
A UART terminal (Tera Term/Hyperterminal), Baud rate 57600.

Running Demo (SDK) Program

If you are not familiar with LX9 and/or Xilix tools, please visit
http://www.xilinx.com/products/boards-and-kits/AES-S6MB-LX9.htm for details.
If you are not familiar with Nexys™3 and/or Xilix tools, please visit
http://www.digilentinc.com/Products/Detail.cfm?NavPath=2,400,897&Prod=NEXYS3 for details.

Extract the project from the archive file (AD5160_<board_name>.zip) to the location you desire.

Avnet LX9 MicroBoard Setup

To begin, connect the PmodDPOT to J5 connector of LX9 board, pins 1 to 6 (see image below). You can use an extension cable for ease of use. Connect the USB cables from the PC to the board.

Digilent Nexys™3 Spartan-6 FPGA Board

To begin, connect the PmodDPOT to JA connector of Nexys™3 board, pins JA1 to JA6 (see image below). You can use an extension cable for ease of use. Connect the USB cables from the PC to the board.

Start IMPACT, and double click “Boundary Scan”. Right click and select Initialize Chain. The program should recognize the Spartan 6 device (see screenshot below). Start a UART terminal (set to 57600 baud rate) and then program the device using the bit file provided in the project *.zip archive, located in the “sw” folder (../ad5160/sw/AD5160.bit).

If programming was successful, you should be seeing messages appear on the terminal window as shown in the figure below. After programming the AD5160 you will be asked to enter a value between 0 and 255, representing the value you desire to load into the AD5160. After you type the desired value and press [Enter] the program will display approximate values for Rwa and Rwb. These values depend on the resistance between A and B (Rab) and the wiper resistance (Rwp).

Using the reference design

Functional Description

The reference design is a simple SPI interface with CS, SCLK and MOSI pins. The information is displayed on UART.

The hardware SPI access allows sending data to the AD5160, programming its internal register with the required ratio between Rwb and Rwa according to Rab and Rwp.

Connecting the PmodDPOT to the boards using an extension cable provides ease of use.
UART must be set to 57600 baudrate.
Please measure the resistance between A and B (Rab) and the resistance between W and B (Rwp) when the programmed value is 0. After measuring please replace the value in ohms in AD5160.c. The approximate values printed on the UART depend on these measured values.

Downloads

Reference design source code for Avnet LX9 MicroBoard.
Reference design source code for Digilent Nexys™3 Spartan-6 FPGA Board.

More information

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Table of Contents

AD5160 Pmod Xilinx FPGA Reference Design

Introduction