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Optimizations for Inrush current

Discussion in 'Electronic Design' started by M. Hamed, May 19, 2008.

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  1. M. Hamed

    M. Hamed Guest

    I have a USB-powered board which draws a lot of inrush current (close
    to 1A) on startup. This leads to problems with the USB interface with
    the computer and also the voltage level droop seen by the devices on
    the board. Now I am faced with the task of figuring out a way to solve
    this problem but I have no clue over how to go about it.

    The board has an FPGA, a microcontroller, SRAMs, EPROM, and plenty of
    discreet components. No power sequencing is done and all the
    regulators turn on at the same time. The board has a TPS2014 which
    helps limiting inrush but seems is not enough.

    How do I go about optimizing the values of bypass caps to reduce
    inrush while maintaining their bypass function? Is there a way to
    simulate that? Are there other ways? Power sequencing is a bit
    difficult because the FPGA uses 3 supplies.

    Thank you.
  2. linnix

    linnix Guest

    What are the V & I on these 3 supplies? You should at least control
    one or two of them?
  3. M. Hamed

    M. Hamed Guest

    The voltages are: 3.3, 2.5, 1.2.

    I'm clueless about two things:

    1) How to measure current drawn from each regulator?

    2) How to sequence power in hardware with no software control. Would
    an RC delay + a transistor work?

  4. Eeyore

    Eeyore Guest

    For how long ?

    The ICs themselves are unlikely to be responsible for that inrush current
    I'd have thought.

    How much capacitance do you have across the various rails. Way too much
    I'll venture.

  5. amdx

    amdx Guest

    I don't know if these inrush current limiters would be slow enough to
    remove your glitch, but worth checking out, or waiting for others to
    give their opinion. My only experience is replacing a smoked one in my
    power supply. Interesting devices!

    Maybe this one? Sheets/SL10 30001.pdf
  6. Jamie

    Jamie Guest

    But Jim, that's to easy and cheap!.. can't you come up with
    something that breaks the budget ?"
  7. M. Hamed

    M. Hamed Guest

    For about 500 us
    around 90 uF on the 5V main supply, and around 22 uF on the 3 other
  8. neon


    Oct 21, 2006
    you can only t out of a USB 500ma so the boaed whatever it is has a bad design solution keep the USB active at all times mine PC is
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