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Original question:

UCC28070: Does any CCM IC support DC input?

UCC28063A: what if the switching frequency is over 500kHz?

Siliang Zhang
Prodigy 110 points
Part Number: UCC28063A

I found that the switching frequency is limited to 500kHz for UCC28063A on the introduction page (http://www.ti.com/power-management/offline-isolated-dcdc-controllers-converters/power-factor-correction-pfc-controllers/products.html#p1694=Interleaved%20PFC&p1131=TM).

What if I use this IC in a higher switching frequency? Will it limit the frequency to 500kHz automatically? If not, what will happen?

Thanks

  • 0
    TI__Guru* 78636 points

    Hello Siliang,

    I reviewed the data sheet for the UCC28063A and can't find where it states the maximum frequency is limitied to 500 kHz.  Could you tell me where that is mentioned?

    The data sheet does gives recommendations that the designs minimum frequency that is chosen is between 25 kHz and 50 kHz for proper oppeaation.  You will select your inductor based on this requirement.

    Based on the minimum frequency you select RT, which determins fmax. In the example of the data sheet it is calculated to be 550 kHz below.

    In the design example in the data sheet the converter should have a freuqency range of 39.2 kHz to 550 kHz. The frequency will vary over line and load to maintain the duty cycle.

    Regards,

    Mike

  • 0 in reply to Mike O'
    TI__Guru* 78636 points

    Hello Siliang,

    Sorry for the issues with large spaces imbetween my response.  I had tried posting multiple graphics into the e2e reply and even though it had done it initialy it did not end up posting them in the reply.

    So in regards to the 25 kHz to 50 kHz minimum switching freuqency (fmin) please refer to  the paragraph above equation 19 in the data sheet and equation 19.

    In regards to fmax being set by RT based on fmin, p[lease refer to equations 48 thourgh 50 in the data sheet.

    Regards,

    Mike

    P.S. I have notified the e2e council about the issues of posting graphics into the reply.  They are working on it and hope to resolve the issue sometime next year.