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UCC28065: UCC28065 driver pin GDA problems

RookieP Soybean
Prodigy 50 points
Part Number: UCC28065

Tool/software:

Hallo,

We are using UCC28065 to build 600W interleaved TM PFC.

But we are facing with a critical problem when we start debugging the circuit.

As you can see in the snapshot below, when we start debugging with 50W @380Vdc load, the driver pin GDA will output several pulses after a normal control pulse. And the inductor current seems to be relevant with these unexpected following pulses:

  • 0
    TI__Mastermind 40350 points

    Hello RookieP, 

    Unfortunately there is no snapshot attached to your post. 
    Can you please repost and add the image using the Insert menu below the text box? 

    Insert > Image/video/file > Upload > (browse for file) > OK

    Regards,
    Ulrich

  • 0 in reply to Ulrich Goerke
    TI__Mastermind 40350 points

    Hello RookieP, 

    Never mind, the image appeared after I wrote my reply. 
    Look like a delayed display or something. 

    I will examine the information and try to figure out what's going on. 

    Regards,
    Ulrich

  • 0 in reply to Ulrich Goerke
    Prodigy 50 points

    Hallo, I have attached the snapshot. Can you see that?

  • 0 in reply to Ulrich Goerke
    Prodigy 50 points

    UCC28065Calculator_password_041813.xlsx

    Hi, Ulrich, Thanks for your attention. Attached xlsx file is our calculation.

  • 0 in reply to Ulrich Goerke
    Prodigy 50 points

    And if we examine the ZCD_A signal, there's an unexpected zero crossing detection positive feedback in time point 1ms. But at that time, ZCD_A should keep in negative voltage. And we measure directly GDA of UCC28065 so that there's no problem with mosfet driver.

    We don't know whether ZCD_A cause unexpected GDA pulses or vice versa?

  • 0 in reply to RookieP Soybean
    TI__Mastermind 40350 points

    Thank you for the Calc file, RookieP. 

    I'll look at it in a little while. 

    In the oscilloscope image, the signal identified as ZCD_A is about +/-10V in amplitude.  This is not the signal at the ZCD_A pin. 
    I assume it is the signal at the ZCD winding.  

    The main GDA signal goes high almost 1us after the ZCD winding voltage crosses below 0V.   There should not be this long of a time delay. 
    You may have excessive R-C filtering on your ZCD inputs.  

    Please post as schematic diagram of the PFC circuit, please. 

    Regards,

    Ulrich

  • 0 in reply to Ulrich Goerke
    Prodigy 50 points

    Hallo, this is the schematic regarding pfc and ucc28065, with some modification which is labelled.

  • 0 in reply to RookieP Soybean
    TI__Mastermind 40350 points

    Hello RookieP, 

    The component values on the schematic at the ZCD pins appear to be reasonable. 
    I recommend to restore R18 back to 22kR and reduce the value of C3 for any fine-tuning of ZCDA timing.  (Same for ZCDB.)
     
    Is it possible that R18 has a 100kR installed (by mistake) instead of the specified 10kR change?   

    C5 bypass cap on VREF is incorrectly connected.  Please correct it as shown here:

    The CS input signal is connected directly to R13, R14 and does not get filtered by R46 & C18.  The "CS-" signal has No Connection.

    I think you intended to have the "CS-" signal go to pin 10 of the IC. 
    In any case, the value of C18 for this R-C filter is much too high. 
    R46 & C18 form a 2.2us delay to detecting peak currents.
    I recommend to reduce C18 value at least to 2.2nF, preferably lower, for effective protection against overload currents.  

    Regards,
    Ulrich

  • 0 in reply to Ulrich Goerke
    Prodigy 50 points

    Hallo, Ulrich:

    Thanks. We will correct Vref and CS drawing on schematic. Nevertheless, since it's only 50W now, we think CS drawing is not the root cause.

    We will try your RC recommendation.

    And by the way, are there any special design consideration for this transformer?

    This is the very transformer (PFC inductor) specification, the turns ratio is 38:2, which is aligned with the calculated results Nps=18.9.

  • 0 in reply to RookieP Soybean
    TI__Mastermind 40350 points

    Hello RookieP, 

    I notice in the inductor spec that the pin locations and sizes are symmetrical.  There is no keying for fool-proof installation.
    My advise is to be careful not to install this inductor in backwards.  

    I hope the other circuit corrects will fix the problem. 

    Regards,
    Ulrich