• State TI Thinks Resolved
  • Locked Locked
  • Replies 2 replies
  • Answers 1 answer
  • Subscribers 64 subscribers
  • Views 400 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

UCC28780: UCC28780

UCC28780: UCC28780

robin gangopadhya18
Mastermind 6296 points
Part Number: UCC28780
Other Parts Discussed in Thread: UCC29002

Ulrich: Let me push it a bit on the application range of UCC28780 ( now that we have the EVM)- can these be put in parallel?

No just 1  but in our case, we would want either 3 in parallel or a multiple of them.

Think of the reason behind triplets & wide applications that open up.

BTW: it dawned on me out of the blue that I should use LGM3410 HB here!

What a wonderful idea....

And, a question: they say you have 2 options for ripple cancellation- passive & active.

Elsewhere, it seems to read like one needs both. Could you pl clarify?

In our mini pkg, every part addition counts. If we can get the same efficiency without some parts,  we will chop them off...

thnx
robin

  • 0
    TI__Mastermind 27145 points
    Hi Robin,

    I will ask Ulrich to help with your questions.

    Best Regards,
    Ben Lough
  • 0
    TI__Mastermind 40580 points
    Hello Robin,

    Like many other SMPS designs using voltage-loop feedback, an ACF converter controlled by the UCC28780 cannot be directly paralleled with another without out some active or passive means to share current. The voltage loops of each converter are independent and each would attempt to regulate a combined output to its own reference. This would lead to oscillatory current between each module.

    More than one ACF converter can be paralleled passively, with series dropping resistors to absorb the voltage differences, but this becomes lossy and negates the purpose of the ACF.
    They can also be paralleled actively using dedicated load-share controllers such as the UCC29002 which senses each output current and adjusts the feedback loop of each converter to achieve tight current sharing.

    Concerning ripple cancellation: I searched the UCC28780 datasheet for the term "cancellation" and found nothing. Searching on "ripple" came up with compensation in several places including the terms active and passive ripple compensation.
    I will make a guess that you are interpreting "compensation" as "cancellation", but this is not the case. There is no cancellation function in the sense of reducing output voltage ripple through a control means. In fact, the UCC28780 requires some degree of ripple to accomplish the Adaptive Burst Mode (ABM) operation. (See sections 7.3.2 and 8.2.2.7 in the UCC28780 datasheet.)

    The passive ripple compensation refers to choosing specific components in the feedback path to enhance the effect of the ripple that is already present on the output. This network helps the optocoupler convert the voltage ripple into FB current ripple used by the ABM.
    In some cases where voltage ripple is very small, the feedback (passive) compensation is not enough and an active ripple compensation circuit (ARC) can be added to the FB node to augment the current ripple content from the optocoupler path.
    Neither of these are ripple-cancellation techniques.

    Regards,
    Ulrich