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About PCI power supply

Discussion in 'General Electronics' started by oxy, Nov 23, 2003.

  1. oxy

    oxy Guest

    If I use 5V connector slot.
    Could I use 3.3v component in PCI add-in Card without any power regulator ?
    please tell me,thanks.

    ps:I had confused with power management long time.

    Best Regards.
     
  2. Ken Taylor

    Ken Taylor Guest

    No.

    Ken
     
  3. Robert Baer

    Robert Baer Guest

    As Ken said, the general answer is "no"; most parts would be desroyed
    by the overvoltage.
    Be safe and use a regulator.
     
  4. oxy

    oxy Guest

    Ya.......it's so bad news!
    but i still have a question for this.
    In PCI Spec,i saw the pins of 3.3v & 5v are in 5-volt add-in PCI card?
    what does it mean? Or 3.3v pin is reserved in 5v add-in PCI card?
    please tell me,thanks.

    Best Regards.
     
  5. Ken Taylor

    Ken Taylor Guest

    What is it that you are actually trying to do? The PCI spec for 3.3V refers
    to the signalling - what you do on the board once the signal gets there is
    your business. However, if you have a 3.3V component you need to supply is
    with 3.3V - regulators are small and cheap.

    Ken
     
  6. oxy

    oxy Guest

    ok ok ~ ~
    I suppose it that 5V slot can't support 3.3v even 1.8v.
    so only I can do is that put 2 regulators to transfer it.
    And I konw regulator is so cheap, but my company wants me cost down do
    my best.
    So in my Rev1.0 PCI add-in card,I must have 2 regulator to support
    3.3v & 1.8v Component to work.
    or Not?
     
  7. Robert Baer

    Robert Baer Guest

    I do not know about the PCI spec, have not looked at it.
    But, if one of the pins is speced at 3.3V, then one might assume that
    it could be used as a power source.
    Just limit the current to 100 mA if possible, with a 500mA absolute
    max surge.
     
  8. Robert Baer

    Robert Baer Guest

    From your questions, it appears that you do not know enough to even
    touch this "project" of yours.
    I seem to remember that at least once, you weer told that seperate
    regulators were needed.
    And if you knew electronics, then you would not have asked that
    question, and would be able to determine if those line(s) that mentioned
    3.3V were signal or power.
     
  9. Ken Taylor

    Ken Taylor Guest

    There are prototyping boards with PCI interface included, with prototyping
    area for you to develop your circuit on. This may be an easier way to do it
    as the VLSI on-board already handles the bus interface.

    Ken
     
  10. oxy

    oxy Guest

    Yesterday,I got news about 3.3v pins in PCI 2.0~2.3 from my teacher(he
    got the news from MB Manufactor).
    He said that if MB is PCI 2.x,so user can use 3.3v power supply from
    5v slot.
    And Imax=4.5A.
    But my boss and teacher tell me that we have to place 2 regulators to
    transfer 3.3v & 1.8v.
    So......it's terrible news for me.....oh!!god!!
     
  11. Ken Taylor

    Ken Taylor Guest

    *Why* is this terrible?? There's plenty of single-component regulators out
    there which will do the trick: eg.
    http://www.sipex.com/products/pdf/SPX5205.pdf
    Two of these, problem gone. And I bet Maxim do a single-chip solution for
    all your power supply levels.

    And don't forget that it's only the bus that's 3.3V so a suitable interface
    chip will remove the bus from the equation.

    Ken
     
  12. Robert Baer

    Robert Baer Guest

    There aint no PCB contacts that can reliably handle 4.5 *amps* !!
    In fact i would not trust a single contact with any current over
    500mA, and it would have to be a multiple contact, *NOT* a single point
    like some Molex connectors.
    Work on the basis of a contact resistance of 10 milliohms.
    Yes, the typical may less, but if there is ever any fault that makes a
    contact go higher, then one certainly does not want I*R heating to
    aggrivate the problem.
     
  13. Robert Baer

    Robert Baer Guest

    Like i have said before *forget* Maxim!
    They do not want to make parts they advertise, unless you have tens of
    thousands of dollars to commit to one of their many un-available parts,
    and 6-20 months of lead time.
    Many distributors refuse to carry any of the Maxim line due to this
    problem.
     
  14. oxy

    oxy Guest

    My company decides to use 3.3v pin to support all component in PCI
    add-in Card.
    So i have to find a power regulator to transfer 3.3v to 1.8v, but the
    IC isn't easy to buy in material store.
    But i don't think it difficult to search.
    The point is how to compute total current in a component (ex. Flash
    ROM,EEPROM,PHY....).
    Although I have spec about all component,but i still don't know how to
    konw total current(it means a component that i need to supply max
    current)
    Can or Could any one help me to answer this stupid question?thanks.
     
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