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UCC28050 (TM-PFC) ZCD current limit value

Toshiyuki Zaitsu
Prodigy 350 points

I have a quesion of  ZCD current limit value, 10mA or 1mA.

In datasheet page 8, "Zero Current Detecion and Re-start Timer Blocks" column, 4th line sentese said;

"The resistor value in series with the secondary winding should be chosen to limit theZCD current to less than 10mA."

Meanwhile, datasheet page 16th, "Zero Current Detection" clumun, second line said;

"This pin (means ZCD pin) has clamp at approximatery 5V.  Add a current limit resistor, RZC, to keep the maximum current below 1mA."

Which of 10mA or 1mA is correct?

Pls advice.

Thanks

Rick Zaitsu 

 

 

  • 0
    Genius 3295 points

    Hello Toshiyuki,

    I have not used this particular IC, however I have designed a ZCD boost converter. Both 1 ma and 10 ma are correct. The 1 ma current limit set for a particular application. Meaning that for that particular example design a 1 ma threshold is sufficient to declare the inductor current to be at the ZCD point. You may have a different coupled winding ratio on your boost inductor (See the schematic on page 10 and observe the component marked L.) so you might want to choose a resistor make the ZCD threshold 3 ma. However, you cannot set your zero current threshold beyond 10 ma or you will break the IC.

    Chuck

  • 0 in reply to Chuck Sampson
    TI__Prodigy 350 points

    Hi Chuck-san,

    Thanks for comments.  It is helpful for me to understand.  For the current value of the specific device, I will check with product line.

    Best regards,

    Toshiyuki (Rick) Zaitsu