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UCC28180: Input current waveform at light load

Shuji Ishiwata
Mastermind 6615 points
Part Number: UCC28180

Hi All,

I have a question about UCC28180.

Customers are evaluating using EVM. The input current waveform has distortion and noise at light loads.
Is this waveform correct behavior?
Is there a way to eliminate the distortion?

Best Regards,
Ishiwata

  • 0
    TI__Mastermind 32940 points

    Hello Ishiwata-san, 

    Thank you for your question on the UCC28180 EVM. 

    I was able to locate an EVM in our lab and spend an hour experimenting with it.  I obtained similar waveforms as shown above, but not exactly the same.

    But I do confirm that there is a resonance in the AC input current at certain phase angles of the line and those resonance points change with load and voltage.  
    The resonant frequency on my EVM was about 13.7kHz.  

    The resonance occurs during certain operating points when the inductor current is discontinuous (DCM = discontinuous conduction mode). 
    It does not happen during CCM (continuous conduction mode).  

    It appears that the phase margin of the current loop is low during DCM.  The ICOMP capacitor on the EVM is 2700pF.  When I applied another 2200pF cap in parallel (from ICOMP to GND) I saw that the resonant ringing amplitude of the current reduced to about 1/2, but did not go away entirely.  
    Possible more capacitance can reduce the amplitude further, but too much capacitance on ICOMP can affect iTHD and phase-shift of the input current (make them worse).   

    I suggest that to minimize this issue, use a higher-value boost inductance and increase ICOMP capacitance.  Test the performance of the PFC (iTHD and PF) at all line and loads of importance to verify compliance with standards.
    I think this can help reduce the resonance, but I don't think it can be eliminated entirely because there will always be some line and load points where the inductor will operate in DCM.

    Regards,
    Ulrich