I have had a slight problem with a design based on snvu111.pdf. 12V in 30V 0.3A out.
http://www.ti.com/lit/ug/snvu111/snvu111.pdf
On startup with no load, the feedback opto is off, but the LM3481 doesn’t regulate the output voltage.
The output voltage reaches a pretty stable 9-10V and stays there.
Do I need to extend the soft start somehow?
I cured it by biasing the COMP pin (which the opto feeds) with a 10K pulldown as well as the 3K3 pullup such that the COMP pin can’t go above 4V.
I wondered if the COMP voltage goes close to its internal 6V rail that the chip goes into a funny state.
Snvu111 does show a DNP component in that position but I assumed that was for a capacitor.
So startup is cured and its stable with transient loads but I don’t know why its cured!!
I would like to understand what is happening.