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Analog Devices isoPower devices (ADuM524x)

Discussion in 'Electronic Design' started by Steve, Feb 13, 2008.

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  1. Steve

    Steve Guest

    We have developed an isolated thermocouple product for industrial
    applications that uses these isoPower devices. The parts work well for
    our purposes but the power supply is horribly inefficient and produces
    severe radiated emissions at 300mHz (integrated PS switching
    frequency) and higher harmonics. We've tried everything from PWB
    layout changes, multi layer boards, ferrites/caps/filters, etc. but
    still have not been able to reduce the emissions to meet the CE
    requirments for industrial environments.

    Anyone have any experience with this part?

  2. John Larkin

    John Larkin Guest

    We used transformer coupled supplies, at 60 KHz with deliberately
    slowed edges, to avoid problems like that:

    Probably cheaper, too.

    We do use their logic isolators, which seem fine, but not the
    self-powered ones.

  3. MHz Presumably ;)
    All the switching currents are within the chip (other than maybe
    transient input) so there may not be much you can do externally to
    reduce EMI. Have you tried shielding it?

  4. D from BC

    D from BC Guest

    Switch to alternative ?

    Maybe check out the various isolators at NVE
    NVE’s IL700 family of high-speed digital isolators are CMOS
    devices manufactured with NVE’s patented* IsoLoop® spintronic
    Giant Magnetoresistive (GMR) technology. The IL710S is the
    world’s fastest isolator of its type, with a 150 Mbps typical data

    Not opto nor RF.

    D from BC
    British Columbia
  5. Apparently I wasn't thinking clearly. A conductive shield across the
    isolation gap might not be very good for the isolation.

    I take it you've implemented there suggestion about providing 100Ohms
    or so of impedance at 300MHz and adding caps to slow down the
    transition edges?

  6. Similar technology to the AD part. I think the problem he is seeing
    is coming from the isolated power supply portion of the chip, I don't
    recall any of the NVE parts providing that. It would be rather nice
    not to have to add a transformer or an Isolated DC-DC but not if you
    can't get past the EMI requirements of course.

  7. John Larkin

    John Larkin Guest

    Some interested party, ADI or TI, published a paper showing that the
    NVE parts are buggy and can get confused about output states.

    I think Steve's problem is with the power isolation stuff, not the
    logic isolator.

  8. qrk

    qrk Guest

    Can you show us a schematic how you tried filtering the noise

    Did your filters have any effect on the noise problem?
  9. asanazi

    asanazi Guest

    Maybe you should forgot about the integrated power converter and build
    external one (or use off-shelve from power-one, Synqor, Tyco, etc.).
    We used ADUM1200 for isolated DC/DC converters as separation of
    synchronisation pulses for rectification; however we also notice that
    sometime, during power-up, outputs doesn't reflect input state. ADuM
    use inductore as isolation barier. Later we replaced with capacitor
    isolators (ISO from TI). Performance is better and there is no more
    "strange" behavior during strat-up. Also MTBF is much better for ISO
    than for ADuM.

  10. D from BC

    D from BC Guest

    I was thinkn:
    Some isolator + clean power = possible solution

    Isn't an onboard 300Mhz converter like trying to have a quiet meeting
    in one room with fire crackers going off in the adjacent room.. :p

    D from BC
    British Columbia
  11. Joerg

    Joerg Guest

    That's the way to do it.

    I mostly use a modulation scheme, essentially a clock and then a DC
    restore (clamping) on the system side. That way there are no
    single-sourced parts in the machine.
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