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UCC28070: Does UCC28070 have a burst operation mode for efficiency improving in light load mode?

Kazuya Nakai59
Guru 20975 points
Part Number: UCC28070
Other Parts Discussed in Thread: UCC28065, UCC28064A, UCC28063, UCC28061, UCC28060

Tool/software:

Hello guys,

One of my customers uses UCC28070 for their mass-production.

At this moment, they have the following questions.
Could you please give me your reply?

Q1. 
They want to improve efficiency at light load mode using UCC28070.
Does UCC28070 have a burst operation mode or phase drop mode for efficiency improving in light load mode?  

Q2.
If your answer is no, do you have any recommended device? Is it UCC28065?

Your reply would be much appreciated.

Best regards,
Kazuya.

  • 0
    TI__Mastermind 45460 points

    Hi Nakai-san,

    Unfortunately the UCC28070 does not have a traditional burst mode. It does have a zero-power detection via the VAO pin which will disable the gate drivers at zero load.

    What is the power level they need to support? The UCC28065 is much better at light load as it will shed one of its phases and being a transition-mode PFC it has much lower standby power at light load. 

    I hope this answers your question. 

    Regards,

    John

  • 0
    TI__Mastermind 34370 points

    Hello Kazuya-san, 

    To answer Q2 first, UCC28065 and UCC28064A both have built-in phase-drop and burst mode functions which improve light-load efficiency.
    Since these operate in Transition-Mode (TM), they may not be practicable to use if the output power is very high.  Your customer must assess whether TM-PFC is suitable for their application, or if CCM-PFC must be maintained. 

    The UCC28070 CCM-PFC controller does not have built-in phase-shed or burst modes.  However, simple external circuits can easily implement the phase-shedding function to improve efficiency.   Here are some documents that describe how to do it with the UCC28070: 

    1200W PFC Ctlr & PT Schematics REVE2.PDF     UCC28070 Phase-Management Demonstration.pdf      UCC28070 Efficiency Gain with Phase-Mgmt.pdf

    To summarize, I recommend to simulataneously disable one of the MOSFET gate drivers, double the IMO resistance, and short-to-PGND the corresponding CAOx output when shedding the phase.  I recommend to use a comparator with the VAO output compared to a user-selected voltage that corresponds to the light-load power level at which the phase-shedding should occur.  Make sure that this level is low enough so that there room for hysteresis and the phase-resume power level still below 50% of full power.  

    Regards,
    Ulrich

  • 0 in reply to Ulrich Goerke
    Guru 20975 points

    Hello John, Ulrich,

    Thank you very much for your reply.

    I will tell them these documents, 
       1200W PFC Ctlr & PT Schematics REVE2.PDF
       UCC28070 Phase-Management Demonstration.pdf
       UCC28070 Efficiency Gain with Phase-Mgmt.pdf

    to support light load mode with UCC28070.

    Also they want to build up 1000W  PFC . (Input: AC90V～264V)

    They chose UCC28060, UCC28061, UCC28063, UCC28065 as the device which can support a burst operation mode or phase drop mode for efficiency improving in light load mode.

    Which device is the best device for light load mode supporting? Is it UCC28065?

    Thank you again and best regards,
    Kazuya.

  • 0 in reply to Kazuya Nakai59
    TI__Mastermind 45460 points

    HI Nakai-san,

    Normally for a 1000W PFC, we see the UCC28070 used.


    The UCC28064A and UCC28065 are the best inherently for light load support, but for a 1000W supply you may find the peak currents are a bit high. As Uli-san mentions, there is an application note showing how to improve the light load efficiency of the UCC28070 at light load.

    I hope this answers your question.

    Regards,

    John

  • 0 in reply to JCHK
    Guru 20975 points

    Hello John,

    Thank you very much for your reply. I got it!

    Thank you and best regards,
    Kazuya.