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UCC28070A: Interleaved 4-Phase operation using UCC28070A

Zaka Zahid
Prodigy 10 points
Part Number: UCC28070A

Tool/software:

Hello,

I am designing a 4-phase interleaved PFC. I have designed the 2-phase version of it. In the 2-phase version, I have used the internal Oscillator. In the 4-phase version, I have to use 180 degree phase shifted external Sync signals. I have designed a 555-timer and D Flipflop based circuit to generate the signals. Can you please review the attached circuit and see if I can use it to generate the sync signals ? Please recommend any changes if the circuit has issues.

Thanks.

  • 0
    TI__Mastermind 40120 points

    Hello Zaka, 

    Overall, your SYNC circuit looks pretty good. 
    I recommend the following modifications: 

    1. Narrow down the time that 555_Out is low to about 300ns wide.  You want the SYNC-x pulses to be as narrow as possible without being less than 200ns. 

    2. Use the upper Schmitt-trigger buffer (at U3-1, 6) to generate a time-delayed signal, instead of a CLR signal.
        U4 does not need to be cleared at power up.  It does not matter which SYNC-x output gets started first... it is irrelevant to interleaving.
    Instead, feed the "CLK" into the RC at U3 pin1 input (in addition to into U4-1).  Configure R3 and C9 values for ~20ns time delay. 
    Change the "CLR" output at U3-6 into "CLK_DLY" and feed CLK_DLY into U5 pins 1 and 5.  
    This time delay into the NOR inputs will allow Q-FF and QB-FF to toggle states and settle before the CLK_DLY arrives so that SYNC-1 and SYNC-2 can be glitch-free. 
    No race conditions with the U4 outputs.  

    Regards,
    Ulrich

  • +1 in reply to Ulrich Goerke
    Prodigy 10 points

    Dear Ulrich,

    Thank you for a quick and detailed response. 

    I have made the suggested changes in the design. Please review them and let me know if I missed anything.

    Thanks.

  • 0 in reply to Zaka Zahid
    Prodigy 10 points

    I would like to add one more question. Is it OK is the amplitude of the Sync pulses is 5V ? I think the internal oscillator generates pulses of amplitude 3V. 

  • 0 in reply to Zaka Zahid
    TI__Mastermind 40120 points

    Hi Zaka, 

    It is okay to run SYNCx amplitude to 5V.  The Absolute Maximum rating of the RDM input is 7V, so make sure there is no significant overshoot. 

    I checked the structure of your redesign.  It looks good to me.  I did not calculate the timing; I assume you can fine tune your prototype during evaluation. 

    Regards,
    Ulrich

  • 0 in reply to Ulrich Goerke
    Prodigy 10 points

    Great!! Thanks.