My goal is to do an isolated Flyback converter from 28V to 3.3V without an optocoupleur for the regulation. First i have simulated my schematic with the controller and the power stage without the isolated feedback ( as a regulation, i was just using a couple of resistor, and the same ground for the primary and the secondary side). I obtained a stable system with Vout=3.3 +-1%.
So, I am trying now to introduce the ADuM3190 Model in my regulation loop. For the schematic i'm using the figure 32 of the datasheet. I put a voltage source of 1.225V to the IN+. EAOUT is connected to the COMP pin of the PWM controller. The FB pin of the PWM controller is shorted to the ground. IN- is connected to the resistor bridge (adjusted to have 1.225 when we have Vout=3.3) and i add a compensation network between IN- and COMP pin.
My problem is that the ADuM doesn't seems to work properly.
When the converter starts, the potential of Vout and the IN- pin are rising but quickly, Vout exceed 3.3 and the IN- exceed the IN+ref of 1.225V, the ADuM output doesn't react and remains at more than 3V during 2ms at least. During this time the converter reaches 18V... Finally after few ms the adum_out fall to 0V, the controller stop and the Vout fall to 0V too. After that, the adum_out rise again and the converter restart. I didn’t succeeded in making the converter to work properly, without this “hiccup” mode.
I don't understand why the ADuM don't react instantly when the Vin- exceed the Vref value ?
See below a link to the schematic and simulation :
Thanks for your support