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UCC28063

Laszlo Lorantfy
Prodigy 150 points
Other Parts Discussed in Thread: UCC28063, UCC28061, UCC28060

Hello,

I would like to design a PFC with UCC28063 (similar to UCC28060, UCC28061). I intend it to work only on high line (so 200-250V AC input). When I do the calculations with the Excel spreadsheet, I got a lower than reccomended (66kOhm) value for RT timing resistior. If I get it right, chosing a low RT value will force the IC to work at very high switching freqs at low load conditions, and if I put n a 66kOhm minimum value in this condition, will force the IC to DCM operation at low conditions?

I read in the UCC28060 datasheet, that it has a low-line and high-line KT value. Is this true for the UCC28063?

My other question is about HVSENSE. Since I don't intend to use PWMCNTL and output overvotlage already sensed, can I put a resistor divider to make it betwwen 2,5V and 4,87V? If I leave it open it will go under 0,8V, due to the current sink, won't it?

Thank you for your answers, anyway.

  • 0
    TI__Guru* 86286 points

    Under light load conditions the transition mode converter will operate at a high switching frequency.  The Rt value will limit the minimum Ton this will limit the maximum switching frequency.  However the FETs will not turn on until ZCD signal is observed.  At lighter loads is the maximum frequency is greater than the on time there will just be more crossover distortion.  This has not been an issue for most customers using this device.

    The only device that has a Kt range change is the UCC28060.  Both the 61 and 63 only have a single range.

    The HVSENSE is a secondary OVP.  If you connect the HVSENSE to a voltage divider you will disable it.