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UCC28950/about current mode and slope compensation

Tsukui Yusuke
Guru 21930 points
Other Parts Discussed in Thread: UCC28950

Hi,

Could you tell me about UCC28950 current mode?

Is there the method to get rid of a function of slope compensation as a state of current mode?
Customer want to disable the internal slope compensation remains in current mode the UCC28950.
Is it possible if customer make RSUM pin a state of OPEN?

Best Regards,
Yusuke/Japan Disty

  • 0
    Guru 21930 points

    Hi,

    Can I get the information ?
    If you need more information or if  I should  clarify my comment ,
    please let me know.
     
    Best Regards,
    Yusuke/Japan Disty

  • 0 in reply to Tsukui Yusuke
    TI__Mastermind 25570 points
    Hello Yusuke-san
    There is an inherent instability in ALL peak current mode controlled power supplies if the duty cycle is greater than 50%. Slope compensation is used to stabilise these power supplies and is necessary for stable operation if the duty cycle exceeds 50%.
    It is also the case that the magnetizing current in the transformer provides some slope compensation, (typically about 10% of the total needed - small but not insignificant)

    The other problem here is that slope compensation will be needed to provide stability when operating in current limit. Even if the UCC28950 is operated in voltage mode, the resistor at the RSUM pin provides slope compensation if the current limit point is reached.

    In summary - I would not recommend operation without slope compensation - and I see no advantage in trying to do so. I would be interested to know why the customer wants to do this.

    Regards
    Colin
  • 0 in reply to Colin Gillmor
    Guru 21930 points

    Colin-san,

    Thank you for your information.
    I understood that you said.
    Customer wants to compensate it for phase with an external circuit.
    So, Customer looked for a method in defiance of an internal slope compensation circuit.

    Best Regards,
    Yusuke/Japan Disty