USB latch-up problem revisited/Attn. Paul

Discussion in 'Asus' started by Jan, Oct 6, 2005.

  1. Jan

    Jan Guest

    I read some interesting comments by Paul about the USB latch-up problem.
    Since I have a P4C800E-DLX mobo I am quite concerned about the matter. As
    Paul explained, one way to avoid the problem is using a PCI-USB card.

    I have the following question: does the problem only occur when hotplugging
    USB devices? In other words: when I power down the system before plugging in
    any USB device, plug in the device and restart the PC, will that be a safe
    way to avoid the latch-up?

    Thanks in advance!

    Jan, Oct 6, 2005
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  2. Jan

    Paul Guest

    I wish I could answer that, but without seeing in print, exactly
    what the failure mechanism is, it is hard to offer advice. The
    advice I give, is intended to be as conservative as possible,
    since I don't really know the answer to questions like yours.
    Intel has not admitted there is a problem.

    Using a PCI USB card means that the Southbridge USB ports no
    longer need to be used. That workaround still cannot offer
    protection for a case of induced ESD discharge, where an
    electrical conductor near the USB ports receives ESD, and
    the energy is coupled into the USB wires. So, even if you
    use only the PCI USB card, I cannot actually guarantee a
    long life for the motherboard.

    There have been a couple of reported cases, where the user
    was not plugging in a USB device at the time:

    "Symptoms:  Machine was running in standby mode.  Hit the
    keyboard to get her going, nothing.  Stated to smell electronics
    burning.  Tried to kill the machine with the button but no
    go.  Then, the machine just shuts down on it's own."

    What that should tell you, is no amount of being "careful" will
    help. Simply stay away as far as possible, from the motherboard
    USB headers and the rear USB ports in the I/O area :)

    Another poster has suggested there could be a manufacturing date
    dependency on the problem. But none of the posters so far have
    reported the numbers printed on the top of their Southbridge
    (or the serial number on the motherboard box, as the first
    two characters are a date code), so we have no way of verifying
    that observation.

    Latchup is a condition where a phantom PNPN junction forms
    between VCC and GND. PNPN is the same structure as an SCR
    (two of which are used in a TRIAC or lamp dimmer). The PNPN
    junction, once triggered by its gate input, continues to
    conduct large amounts of current until the voltage across
    it drops to near zero. In the case of the phantom PNPN structure,
    it appears when more than a certain amount of current is forced
    to flow into an input. Mechanisms that can cause this critical
    amount of current to flow, are a static electric discharge,
    but also an inrush current can do it too. ICs typically start
    to have input latchup problems at 500mA to 1A of current
    jammed into or out of an input lead. That amount of current
    is much larger than the normal current levels used for most
    logic functions.

    Paul, Oct 6, 2005
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  3. Jan

    Jan Guest

    Hello Paul,

    Thanks for your (as always) educated answer to my question. I always
    appreciate reading your answers and I must say you are a great credit to
    this newsgroup.

    I googled on the matter today and I recognize your quotes mentioned above.
    It really appears to be a very complicated matter, because neither Intel or
    Asus seems to be willing to admit there is a serious problem with these
    chipsets and therefore it's hard to understand what causes the "meltdown".

    I think I will install a PCI USB-card, just to be sure. Could you recommend
    any brand or type? I live in the Netherlands and this means of course that
    not all of the products available in the US will be available here. I also
    want to buy a USB hub to overcome the problem of all the USB ports being
    situated at the rear of the case after installing the card. Any suggestions
    on that will be appreciated as well.

    Thanks again Paul!

    Jan, Oct 6, 2005
  4. Jan

    Paul Guest

    NEC USB chips seem to have a good reputation. The best way to
    find them, is find a web site that has pictures of the USB
    cards, and see the chip in the picture. Adaptec USBConnect
    cards use NEC chips, and there are probably others.

    (Microsoft developed their USB 2.0 drivers, using NEC chips. The
    reason was that NEC was available first, AFAIK. Since there
    are standards for USB design, the chips really should not
    differ in operation, but they sometimes do.)

    There is a fairly large list of USB and Firewire cards here.
    I typed in Adaptec in the "add-in card" search box, and got a
    few hits. You can click the pictures and eventually get to
    see a detailed picture.

    For example, this four port card:

    uses a NEC chip. You need to download the picture and zoom in
    with a picture editing tool, to see the word "NEC" on the chip.
    (Other suppliers of chips are VIA and ALI.) 2.0 PCI card Model USB2connect 4000 - Retail

    As for USB hubs, I really don't know which ones are good.

    Paul, Oct 6, 2005
  5. Jan

    PL Guest

    Jan wrote:

    I would like to endorse that sentiment.
    PL, Oct 6, 2005
  6. Jan

    Jan Guest

    Many thanks Paul, I will investigate the links you provided.

    Jan, Oct 6, 2005
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