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Original question:

UCC28064A: Difference between PUCC28064D and UCC28064ADR

UCC28064A: ZCD VOLTAGE

Jiahui Jiang
Prodigy 30 points
Part Number: UCC28064A
Other Parts Discussed in Thread: UCC28064, TPS92314, UCC28060

We plan to use UCC28064A to implement a single-stage flyback PFC, while the output voltage is adjustable. However, we have encountered a problem that the voltage of the ZCD pin may become lower due to the output voltage adjustment. We are not sure how UCC28064A handles the ZCD internally. If the voltage of the ZCD pin is lower than the threshold of the internal comparator, will the chip not work or work in some form?

  • 0
    TI__Guru 71435 points

    Hello,

    I am reviewing your inquiry and will get back to you shortly.

    Regards,

  • 0 in reply to Mike O'
    TI__Guru 71435 points

    Hello,

    I don't think the UCC28064 is the best option for a single stage PFC flyback.  It was designed for transition mode interleaved PFC boost converters.

    I would recommend the TPS92314 transition mode PFC flyback controller instead.  The following link will bring you to the TPS92314 data sheet.

    https://www.ti.com/lit/ds/symlink/tps92314.pdf

    If you decide to use TPS92314 in your application and have questions, please repost in the e2e with TPS92314 so the appropriate applications engineer can answer your questions.

    If this resolved your issue, please check resolved at the end of this thread.

    Regards,

  • 0 in reply to Mike O'
    Prodigy 30 points

    Hello,

    TI has a application report. SLUA625 – October 2011  LED Driver Based on UCC28060 Interleaved ACDC Single Stage Flyback.

    I think UCC28064A is also suitable, but what we want is a wide range adjustable output voltage, which may cause problems with ZCD pin detection. Perhaps I have roughly obtained the results from the data manual. If the ZCD voltage is always less than 2V, the PWM will automatically restart after a period of time.

    Regards,

  • 0 in reply to Jiahui Jiang
    TI__Guru 71435 points

    Hello,

    I am reviewing your inquiry and will get back to you shortly.

    Regards

  • +1 in reply to Jiahui Jiang
    TI__Mastermind 30370 points

    Hello Jiahui, 

    Mike is out the office today, so I will try to answer your question for him. 

    The ZCD inputs of the UCC28064A (and similar devices in this controller family) have two thresholds: the arming level at 1.7V and the trigger level at 1.0V.
    For the controller to function properly, the ZCD voltage must rise higher than 1.7V first , then fall lower than 1.0V second in order to trigger the next switching cycle.  If either of these two thresholds cannot be crossed for any reason, then consecutive switching stops.  

    Because this situation can sometimes happen in the usual PFC applications (such as at the peak of very high-line input), these controllers have an internal "watchdog" timer which automatically generate a start or trigger pulse after a non-switching dead time of ~210us, to try to restart the PFC.  
    Because this timer cycles only every 210us, it is unsuitable to rely on for PFC whether normal boost or single-stage configuration if the ZCD signal is continually out of spec. 

    So the short answer to the question is: If the voltage of the ZCD pin is lower than the threshold of the internal comparator, the chip will not work.

    Regards,
    Ulrich