A bias winding is needed in order to utilize the HV self start up function. It is recommended to design the bias winding so that the VCC voltage is greater than 13 V.
The transformer can be built or purchased according to these specifications:
The minimum operating frequency during normal operation is calculated above. Please note that for some applications that operate as a wide input LLC where the PFC may be shut off in standby mode, the operating frequency may be much lower during heavy load shutdown and the LLC can operate at just above the ZCS boundary which is a lower frequency. The magnetic components in the resonant circuit, the transformer and resonant inductor, should be rated to operate at this lower frequency.