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UCC28730: 12V@0.5A 40-120VDCIN buck converter based on PMP22557 & PMP22487

Part Number: UCC28730
Other Parts Discussed in Thread: PMP22557, , PMP

I require a 12V supply with a wide voltage input range. I have used the reference designs and recalculated values for 12V & 0.5A output current.

Can someone please double check to make sure I have the correct values and if the converter will startup?


  • Hello,

    What reference design did you use?  How and what devices did you modify and why?


  • The schematic is mainly based on reference design PMP22557.

    The voltage sense resistors (R60000, R60004) we calculated using the formulas in the UCC28730 datasheet Section 7.3 and using a 'transformer ratio' of 1.

    Similar current sense resistors (R60002, R60005) were calculated for 0.5A.

    The input filter (everything left of C60006) was added to allow AC & DC voltage input

  • I doubled checked the calculations and picked up some errors. The schematic is now as shown.

  • Hello,

    It looks like this is copy of the PMP22557 schematic so functionally this is correct.

    The output inductor and current sense resistor should have changed for a 0.5 A value.

    The calculations in the data sheet are for a flyback.  When I talk to designers of the high side buck converters using PSR controllers similar to this one, they drive them deeper into discontinues mode.  So the inductor calculations may not be exact.  No one has written and application note on this so I do not have equations to share.  However, I do have some advice and believe you can scale this design.

    Use the 0.4A/0.5A ratio to resize the inductor and current sense resistor.   

    L = Lpmp_2257*0.4A/0.5A


    When it comes to selecting capacitors and RMS currents use the 0.5A/0.4A ratio.  This will allow you to scale the design up for the higher power.  This should work for the peak current as well.  You will have to look up all the components of the PMP design to figure out what the peak and RMS currents are.

    Irms = Irms_pjmp2257*0.5A/0.4A.