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UCC28019: Magnetics, clarification and sourcing

DENNY Esterline
Prodigy 20 points
Part Number: UCC28019
Other Parts Discussed in Thread: UCC28180

I'm currently trying to implement a PFC solution based on the UCC28019. I have the UCC28019EVM unit and I'm being tripped up by the magnetics.

The EVM BOM calls out a 1.25mH inductor. The inductor on the board is physically HUGE. (2.5 inch diameter torroid, about 1 inch thick) I ordered some 2 and 4 mH inductors from my usual sources and they are much smaller (one inch largest dimension).

I've done a few tests on the EVM with moderate load (operates as expected), significant overload (surprisingly well behaved).

Now I've swapped the inductor for one of my off-the-shelf units (DENO-25-0001) and attempted to test the (now modified) EVM again.  It will not hold output voltage with even half rated load.

So, I'm confused. Either one of these datasheets is lying to me about the size of the inductor, or there's another factor I'm missing somewhere. I'd appreciate a bit of guidance. My suspicion is that there's something about the ferrite composition of the supplied inductor, but I cannot find a proper datasheet for it, so... 

This is for a very low volume product (less than 50 pcs/yr) so stock magnetics are greatly preferable.

Thanks

  • 0
    TI__Mastermind 34465 points

    You need to check the peak current rating of both of these inductors.

    The size of the inductor is proportional to the L value and the square of the peak current.

    You can use the calculator tool to calculate the inductance and peak current requirement for your application.

    It looks like the inductor you found does not have the peak current capability required for your application.

    Regards,

    John

  • 0 in reply to John Griffin1
    Prodigy 20 points
    That's at least half the problem. The only published information I can find on the inductor supplied with the EVM is this line in the BOM:
    L1 1 Inductor, PFC boost, 1.25 mH, 7 A, 2.500 Dia. Vitec AF4699-111306
    Searching the Vitec part number finds it in a listing page, but no link to datasheet, just "(call)".

    The Deno part I tried actually does have a datasheet, the relevant specs there are 4mH, 16A, 27mOHM, and 300kHz resonant frequency.

    As mentioned, this is a low volume product, so custom magnetics would be pretty painful. Suggestions for purchasable off-the-shelf parts would be much appreciated.


    Actually, thinking this through, I'll open up a second "suggestion request"... This is a low duty cycle (5 minutes per hour) motor drive that averages about 300 watts and will have short term (30 seconds) peak load of near 1kW. There is a separate power supply for the logic side of the unit and it could easily be tapped to provide control power for the PFC solution. Is the UCC28019 the best option I have, or am I missing something better?

    Thanks,
    -Denny
  • 0 in reply to DENNY Esterline
    TI__Mastermind 34465 points
    Hi Denny,
    I have one suggestion.The UCC28019 is an older generation part that runs at a fixed 65kHz frequency. The UCC28180 is a newer part with advanced features and it has an adjustable switching frequency with 250kHz maximum value.
    This allows you to use a much smaller inductor. The UCC280180EVM switches at 120kHz and has a 327uH, 7.7A peak rating.
    The datasheet shows how to calculate the inductance value. The inductor used gives a ripple current of 40%
    If your system can tolerate a higher ripple current then the inductance value will be lower.

    The inductor you tested is not suitable for pfc applications. The 16A rating is simply the fuse or fault rating of the wire used and does not relate to the magnetic saturation of the core.
    Finally the duty cycle rating (5 mins on per hour) mean that you will need to calculate the peak current rating at 1kW and the average current rating at 83.3W. This most likely means that the peak current will dominate the inductor size.
    I suggest that you calculate values for inductance and peak current capability and then contact a magnetics manufacturer for parts.
    Many of the parts they manufacture are not listed on their websites.
    Hope this helps.
    Regards,
    John