JAJSE40A October 2017 – February 2018 UCC28780
After NPS is chosen, LM can be estimated based on minimum switching frequency (fSW(MIN)) at VBULK(MIN), maximum duty cycle (DMAX), and output power at nominal full load current (PO(FL)). KRES represents the duty cycle loss to wait for the switch-node voltage transition from the reflected output voltage to zero. 5% to 6% of KRES is used as a initial estimated value. The selection of minimum switching frequency (fSW(MIN)) has to consider the impact on full-load efficiency and EMI filter design.