I made a supply for 3.3V, 4A max. This runs of a 24V +/-10% supply. I used the webbench to design the supply and ended up with this design:
Although the supply is designed for max. 4A, it is normally loaded at 0.5-1A.
The problem I have now is that the output is about 3.58V. If I measure with an oscilloscope on the feedback pin, I can see the voltage goes from just below 600mV up to 720mV, after which the overvoltage protection is triggered. This does indeed limit the output voltage.
I tried limiting the on-time Ton by using a smaller Ron, giving me the following results:
- Ron=75k -> Ton=430ns
- Ron=62k -> Ton=410ns
- Ron=47k -> Ton=370ns
Then I soldered in a 10uH inductor instead of the 6.8uH inductor, giving me the following results:
- Ron=47k -> 330ns
- Ron=33k -> 300ns