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Altera_Forum
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8 years ago

Driving Ladder DAC

Hi, Im trying to drive a resistor ladder DAC from my DE-1 SOC board, despite of my DAC being very accurate im getting somewhat shotty results. The setup is relatively simple driving the resis...
Altera_Forum's avatar
Altera_Forum
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8 years ago

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I found the menu responsible for this in the pin planner. According to "this page" (https://www.altera.com/support/support-resources/knowledge-base/solutions/rd01112011_164.html) there is no way around this. Also there is nothing useful in the "pin connection guidelines" for cyclone5 devices..

So is there a way to remedy this?

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That indicates that before a device is configured, and during configuration, the weak pullups will be enabled on the I/O pins. However, you can configure the I/Os to have no weak pullup and no bus hold, so a output that is disabled will only source the leakage current (between -30uA and +30uA per datasheet). BTW 30uA at 3.3V is about 110K effective ohms (minimum; will be higher for lower currents) so even with the weak pullup disabled there will be a pullup/pulldown of something on the order of 110K to 220K or so ohms per I/O.

Picture of the I/O structure:https://alteraforum.com/forum/attachment.php?attachmentid=15362&stc=1