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SmartMedia Card will crash my system ?

Discussion in 'Electronic Design' started by Guest, Jun 24, 2005.

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  1. Guest

    Guest Guest

    Hi All,
    I enconuter a big problem, when I insert a SmartMedia memory card
    to my system, my system power will be shifted, the VCC will be shit down to
    ground abruptly and then reutrn to VCC, the ground is doing the same thing,
    from 0V to -5V.

    my system ( embedded system ) will crash after that, in my case, it will
    auto reset ( restart) when I insert SmartMedia card, but it will not happen
    every time, but it happens.

    I main chip is running 5V, other components is running at 3.3V.

    Could you please give me any hints?

    Thank you very much!

    Best regards,
  2. One day got dressed and committed to text
    Words fail me !!
  3. Guest

    What are these voltages measured relative too? Where is the ground
    lead of your scope probe connected? If part of your ground net (with
    the probe tip) is reading -5v relative to another part (with the ground
    clip) you have a serious problem! Are there even any negative power
    supplies in the system?

    If it were only the VCC dropping, it would seem like an inrush current
    issue. I'd try another smartmedia card if one were available. Also
    would considering putting together something to power up the card with
    no signals connected, with a small series resitor in the ground lead to
    it, and measure the voltage across that resitor, hence the startup
    current. You should expect some startup current, which would be
    supplied by capacitors located close to the card socket, but it
    shouldn't be huge.

    But what you are seeing in the ground suggests something more
    systematic is wrong with the circuit or your measurement setup.
  4. rebuild the power supply, or find out why the SM is drawing enough
    current to put the PSU into shutdown.
    What is the maximum current the supply can deliver?
    What are the startup parameters for the SM card
    Are the 3V3 componets 5V tolerant?

  5. it's a wikiBoki post(TM), they normally arrive on fridays

  6. Boki

    Boki Guest

    I didn't go to make sure the 3V3 componets have 5V tolerant or not yet.
    Due to I can see the supply voltage will become lower than 5V( maybe 2V,
    3V..whatever), I think that is a big issue, because my main chip (CPU) is
    woking on 5V supply voltage, the others DRAM/UART/xxxx/... I think it maybe
    not so important at this time, how about DRAM? will DRAM cause system reset

    current is a good point.

    one possible thing, the system will not( or very few) be reset before I add
    EMI circuit/beds..

    Best regards,
  7. Boki

    Boki Guest

    Does it possible if I add circuit that enforece 3V3 stronger? I mean, make
    my 3V3 will not be shifted any more.

    I hope I can do it in a simply way.... it is going to mass
    [email protected]@@@@@~~~~~~
  8. Boki

    Boki Guest

    How about "Word beats me" ?

    Best regards,
  9. Boki

    Boki Guest

    The maximum current can supply by adapter is about 1000mA, it is working on
    about 500mA.

    Best regards,
  10. Boki

    Boki Guest

    It seems to be a big problem! We have no negative power supply.

    What I were amazed is my old version circuit( without EMI circuit ) also
    encounter this problem, but it almost never reset...

    Please review this picture:

    green line is VCC, yellow line is GND, (2V/grid in scope)
  11. Guest

    Picture won't open for me.

    But I ask again, what is the voltage of ground being measured relative

    Where is the ground lead of the scope probe connected to the circuit?

    You are using a ground lead, right?
  12. nice picture
    where is it?

  13. I missed this at the first look at your post
    You are measuring it _incorrectly_. As cs_posting suggested
    Check your grounding carefully. There should be no V on the ground
    You have the scope probe ground on a point that IS NOT GROUND.

  14. James Meyer

    James Meyer Guest

    Words now fail ME!

  15. Boki

    Boki Guest

    Taipei 101 :)

  16. Boki

    Boki Guest

    I am very sorry about that.

    I am using something like this(but not this one):

    and I measure the ground relative to the embedded system's ground.

    The crocodile(?) clip of picture is connecting to system's ground, and the
    probe is connect to the ground of components. ( they should the same
    [email protected]@)

    I use one probe to measure the 3V3 and the other one to measure GND...

    Best regards,
  17. Boki

    Boki Guest

    Hi Martin,

    "no V", do you mean 0V?

    Yes, the ground is 0V, I just take some offset..

  18. Guest

    Now that the picture will display (at least sometimes) your problem
    becomes more clear. Your 2Gsample scope is fast enough to capture the
    full ugliness of the few nanoseconds long transient that results from
    plugging in the sim card, and the subsequent ringing as it bounces
    around for a total of perhaps 15 nanoseconds. A classic 20mhz
    bandwidth hobbyist scope would probably show none of this.

    But the fix is simple. Modern electronics do nasty things like this
    every time they switch, not just on power on. CMOS is particularly bad
    - it consumes almost no power sitting there, but when it switches it
    practically shorts out the power supply, but only for the briefest

    The solution is to provide a miniature power supply for each part of
    the circuit, located immediately adjacent to the device it services so
    that there are no resisteive or inductive imdepiments to providing the
    needed power immediately. This miniature power supply is called a
    bypass capacitor. In the days of through-hole components, you'd see a
    little .1 uF cap placed right at the end of each IC. They are still
    there in the surface mount era of course, but harder to identify. In
    the vicinity of the clock edges, those tiny little bypass caps are
    *the* power supply for the circuit, while in between the clock edges
    they are recharged from the larger filter caps and the external power
    source of the circuit.

    So here's the fix:

    - Place a bunch of low series resistance .1uF caps right at the card
    socket, as physically close as possible.

    - Place some larger, 1-10uF low series resistance caps somewhere close

    - Ideally redesign the board with ground and power planes, or at least
    short fat power traces to minimize their resistance and inductance for
    feeding everything else on the board (though you may want some
    impedance in the supply to the card socket, see below)

    One might think that the bypass caps belong in the removeable card
    itself. And there probably are some in there, but they are actually
    part of the problem you are experiencing: when first plugged in, those
    uncharged caps constitute dead shorts across the power supply! You
    have to have enough charge stored in caps right at the socket to fill
    them up, so that they don't send undervoltage pulses bouncing through
    power traces that would constitute a nightmare in terms of
    radio-frequency analysis.

    If none of that works, a more extreme measure would be to power the
    card socket and it's bypass caps through a series resistor or inductor
    to limit that startup current. If this causes problems in operation of
    the card, the final extremity would be to soft-start the card through
    such a series limiting element, and then close a switching device to
    take it out of the circuit a few ms later.

    Oh, and it's not just the card socket that needs bypass caps - every
    other IC does too, often a handfull in the case of a modern processor.
  19. Boki

    Boki Guest

    Dear CS,
    I am very thank you for your help.

    I have to update my problem:

    1. The shifted VCC is huge, but it seems that not the main reason about
    system reset. ( sometimes I got huge shift between VCC and GND
    (cross...), but the system still work stable..)

    Question 1: The vabiration time is about 5ns~10ns, is that a safe time
    for .25um process or .5um process CMOS ?

    2. We put all ground together... it seems that a big problem. I will
    cut the Card reader part tomorrow.

    3. Does it help if I add L between GND points?

    Thank you all very much.

    Best regards,

  20. Boki

    Boki Guest

    1. GND + L to system's GND
    2. Change #SM_CD be detected in the last mile.
    3. VCC + L to system's VCC

    Boki 寫�:
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