I am trying to use the LT3757 as a flyback converter. I am generating 200V from 5V (<10mA). I am having issues with the transformer I selected. Since the transformer in the reference design (DCT15EFD-U44S003) is obsolete I went with the ATB322524-0110-T000. I can generate the appropriate voltage but when I use 1 MHz switching frequency the transformer get really hot and in some cases fails and melts. I was hoping you could direct me to a transformer that has similar specs to the one used in the reference design.