UCC28056: Ton Calculation

Hello Renan,

Thank you for your interest in the UCC28056 PFC controller.

The term δONDCH(θ) is a duty-cycle factor of the combined on-time plus discharge time with respect to the switching period at any given phase angle of the line voltage.    δONDCH(θ) =  [TON(θ) + TDCH(θ)] / TPER(θ), as seen in equation 3 (page 16) and illustrated in Figure 19 under DCM operation.  This factor = 1 when in CrM operations and < 1 when in DCM.

GFF is a Feed-Forward gain factor defined as the square of the ratio of the peak level of the minimum input line voltage to the peak level of any given input line voltage.  So when the input voltage is the minimum input voltage, GFF = 1.  For any higher input voltage, GFF will be < 1.  As explained in Section 8.3.2, GFF is actually quantized into 8 discrete values (separated by 7 rising and 7 falling thresholds).  These quantized gain values help keep the overall voltage-loop gain more constant within 20% of the nominal gain, across the minimum to maximum input line voltage range. 

VInPkL is the peak level of the input voltage (presumably a rectified sine wave).     

Regards,
Ulrich