The maximum operating frequency in a given application can be approximated from the primary transformer inductance, the windings ratio (NPS), the nominal output voltage and the maximum input voltage. Unless the part is limited by minimum on- or off-times, this maximum frequency will occur when the part is regulating in boundary mode at the minimum peak switch current, and can be derived from: f SW(MAX)≈ VIN(MAX) •(VOUT + VF(DIODE))•NPS LPRI •ILIM(MIN) •((VOUT + VF(DIODE) )•NPS + VIN(MAX)
