ZHCSNG6 November 2021 UCC28781-Q1
PRODUCTION DATA
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 highest nominal output voltage, nominal full-load current (PO(FL)). The choice of fSW(MIN) should consider the expected range of switching frequency as bulk voltage increases from minimum to maximum and as load falls from maximum to the burst mode threshold. KRES represents the duty cycle loss to wait for the switch-node voltage transition from the reflected output voltage to zero. Typically, fSW may extend to 200% to 300% fSW(MIN) or higher. A KRES value of 5% to 6% is used as an initial estimate for GaN-based power stages, while ~10% is more appropriate for Si-based designs. The selection of minimum switching frequency (fSW(MIN)) should consider the impact on full-load efficiency and EMI filter design.