Is it possible to design a micro current isolate power like that? Vin = 10V, Vout = 5V, 20mA < Iout < 50mA, and the most important efficiency must above 70% . I want to use a PFM DC-DC controller to achieve that. Anybody can give some suggestions on choose the PFM DC-DC controller? how about buck like TPS40210 \ MAX639 or boost MAX608 ?