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AR# 22917

Spartan-3/-3E - Why does Xilinx recommend driving PROG_B with an open-drain output?

Description

The Spartan-3E Data Sheet recommends driving PROG_B with an open-drain/collector. This was not mentioned in the Spartan-3 Data Sheet.

Why does Xilinx recommend driving PROG_B with an open-drain/collector output in Spartan-3/-3E?

Solution

It is recommended that you use an open-drain/collector with a 4.7k pull-up resistor to drive PROG_B because it allows you to control PROG_B with multiple sources (i.e., Micro processor, and push button). For 3.3V configuration, pull the open-drain to 2.5V to keep the internal Power diode from turning on.

This could be applied to Spartan-3 or other FPGAs as well. The motivation for adding this note to the Spartan-3E Data Sheet is to just add extra guidance from an applications perspective.

AR# 22917
Date Created 09/04/2007
Last Updated 12/15/2012
Status Active
Type General Article