UCC256304: UCC256304 can supply input 160VAC-264Vac

Hello Jack,

Thank you for your interest in the UCC256304 LLC controller.

LLC converters are popular due to their high efficiency, but this is true mainly for a narrow input range and a fixed output voltage. A wide-range input can be accommodated but at significantly reduced full load efficiency at the voltage extremes. A wide output range in addition to a wide input range compounds this problem.

To get the best performance from the LLC converter, it is preferable to keep the AC input range as narrow as possible. Remember that the rectified AC has a lower DC minimum valley voltage than the lowest AC peak voltage. For 160Vac-264Vac input, the rectified DC is likely to range from 180V to 373Vdc, since the valley voltage must be included in the low-to-high input voltage range.

For an input variation of about 2:1 and an output variation of 2:1, the controller must accommodate a gain range of about 4:1. The appropriate gain curves (see application note: www.ti.com/.../slup263.pdf) are chosen based on the maximum input minimum output, and minimum input maximum output voltages. That application note was written for the UCC25600, however, the design principles for determining the Ln, Qe and Re are the same and apply to the UCC25630x family as well.

I recommend to follow the UCC256304 datasheet design procedure because the UCC25630x Design Calculator Tool (SLUC634B) was developed on assumptions of narrow PFC input range and fixed Vout , not for wide ranges of Vin or Vout. The datasheet equations are not limited by the calculator tool presumptions. Also, the SLUP263 app-note contains design curves that the datasheet does not.

Regards,
Ulrich

thanks for your reply.