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UCC28220: Technical issues for interleave forward topology

Benjamin Zhou
Expert 4000 points
Part Number: UCC28220
Other Parts Discussed in Thread: LM5034

Hi Team,

  My customer now is looking for suitable solution for interleave forward topology which used UCC28220 for the first version, but reported some technical issues, could you kindly help on below items?

Input Range:  200V~900V(OVP is 980V);

Output Range: 50V@10A(OCP is 15A);

Specific requirement: Support primary PCMC(CBC) with OTP; 

  1) Suggest a suitable device for UCC28220 replacement;

  2) if with UCC28220,  how to limited the maximum duty cycle?  currently used adjust the resister which connected with SLOPE and GND to limited the duty cycle(currently 47%),  could you kindly give comments on the duty cycle limitation with currently solution?

  3) In light load,  UCC28220 worked as burst mode,  the OUT1 with maximum duty but the OUT2 is in variable switch frequency mode,  which created the OUT1/OUT2 capacitor disbalance.  Could you kindly share the UCC28220 work flow for how the 2 different phases adjust the shared current or do the voltage balance? 

Expect for your kindly reply, thanks.

Best Regards

Benjamin

  • 0
    TI__Intellectual 2640 points

    Hi Benjamin! 

    Thanks for reaching out and for your strong customer support! What kind of problems is the customer experiencing here? 

    Another star interleaved forward converter controller we offer is the LM5034, take a look at it and see if it may fit here. 

    The procedure for limiting the maximum duty cycle is described in Section 8.3.3 of the datasheet. A specific design example is also featured in Section 9.2.2.4. Rchg is the resistor between the CHG pin and GND and Rdischg is the resistor between the DISCHG pin and GND. How is the SLOPE pin involved with this? I would think that it wouldn't need to be connected. Are you trying to vary the set max duty cycle based on the SLOPE value? 

    Thanks again for getting in touch, I look forward to talking more! 

    Aidan Davidson

  • 0 in reply to Aidan Davidson1
    TI__Expert 4000 points

    Hi Aidan,

      This is for new design which customer has experience on the UCC28220.

      There are 2 topics:

      1) Maximum duty:  Resister for CHG & Resister for DISCHG are used for maximum duty limitation which has mentioned in datasheet,  this has been discussed with customer, 

       Currently customer used SLOPE resister to limited the maximum duty to <50%,  Could you kindly share your comments on this implementation?

      2) Light mode operation mechanism:  how the UCC28220 to control the 2 phase in light load or no load condition?  is the 1 phased disabled and only 1 phase controlled? or there is share current ways to control both the phase in light load or no load?  How the PWM duty dispatch?

    Expect for your kindly reply, thanks.

    Best Regards

    Benjamin

  • 0 in reply to Benjamin Zhou
    TI__Intellectual 2640 points

    Benjamin, 

    The value of the SLOPE resistor should have no impact on the maximum duty cycle limit. 

    What is the CTRL pin voltage when you are observing the channel mismatch? If the CTRL voltage starts to drop to 1V or below it could be possible that due to mismatches between the two channels that one channel starts to provide the largest portion of power.

    Thanks! 

    Aidan

  • 0 in reply to Aidan Davidson1
    TI__Expert 4000 points

    Hi Aidan,

      Sorry to reply so later， and I moved this discussion with mail discussion,  so I closed this post.  Thanks for your support.

    Best Regards

    Benjamin