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Altera_Forum's avatar
Altera_Forum
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16 years ago

Voltage Regulators for Cyclone III

Hi. I want to use a LM317 regulator to feed my EP3C16Q240C8. The problem is that the minimum voltage the regulator is able to output is 1.25 V while the core voltage for the FPGA is 1.2 V. Is this small voltage difference ok or should I look for another chip?

thanks,

Lambros Gavriilides

2 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    16 years ago

    This might work, but I would strongly urge against it, especially since you are talking about the core voltage. There is practically no margin left on the high-end of the rail. Even if regulation is perfect, the part will run warm.

    Perhaps I'm a bit more conservative due to the line of work I'm in, but I try to aim for the center of the spec if possible. It's also kind of silly, since you can get 1.2V fixed linear regulators for about $1-2 capable of sourcing several amps of current.

    (http://search.digikey.com/scripts/dksearch/dksus.dll?detail&name=fan1112sxct-nd)
  • Altera_Forum's avatar
    Altera_Forum
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    16 years ago

    I've seen many designs, that used a 1.25V regulator for 1.2V. But by specification, it doesn't guarantee to keep the Cyclone III voltage range. If you expect additional 50 mV voltage drop at filter chokes or PCB traces, it would be just O.K.