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Original question:

UCC28950: End of project of 7kW dc everthing is ok!

UCC28950: Question about COMP pin

Lin_Charles
Expert 4260 points
Part Number: UCC28950

Hi team,

   I want to know in which condition UCC28950 will have maximum duty output?

  • When V(comp)>2.8?
  • When V(comp)>2.8+0.85?

    And I would appreciate it if you can share me the reason why we have 0.85V offset voltage in below picture. Thanks a lot!

  • 0
    TI__Mastermind 25570 points

    Hello Charles

    The controller will run at Dmax when COMP reaches 2.85V.

    The 850mV offset symbol represents the RAMP signal offset shown in the block diagram where the signal amplitude is given as 0.8V/2.8V. The offset is implicitly shown in the block diagram and explicitly shown in Fig 36 but it's the same offset in both cases (rounded to 1 place of decimals in the block diagram). The usual reason to add such a fixed offset into an analog circuit is to make sure that all of the circuit's linear operating range is available for use. For example, if you were using an external error amplifier and configured the UCC28950 error amplifier as a voltage follower then you do not have to worry about the ability of the output of the external amplifier to pull down to 0V - the offset means that the external amplifier has to be able to pull down to 800mV which is much easier to guarantee.

    In practice this offset is 'invisible' to the control loop and the designer will not have to worry about it.

    I hope this answers your question, if it does not then please let me know.

    Regards

    Colin