WEBENCH® Tools/TPS54560: Checking my understanding

Howard,

Yes, the red boxes are warnings. You can see a description of the recommended inputs if you hover over the red area (or any of those values). See picture below.

For this part we recommend a Low Freq Gain of >70dB so the original 62dB gives you a warning.

I've recompensated and found the same result as you. It's suggesting parts that give insufficient phase margin and gain margin (insufficient for our tools may not mean insufficient for your application).

Go back into Re-Comp and use the Optimization Tuning slider. Move it all the way to the right toward Performance. That should give you comp values with no warnings.

-Sam

Howard,

Phase Margin: I like to shoot for between 45 and 60 degrees. Lower will recover faster in load transients and such but faster means more overshoot in the recovery. Too low means the overshoot will get worse and ring.

Gain Margin: -10dB is good but a greater negative (-20dB) is better.

Crossover Freq: This is how quickly your system will respond to a transient like load transient. Higher is better because it's faster (meaning less time for VOUT to stray from regulation meaning less under/overshoot). But too high might cause problems. Stay under Fsw/10. I like ~20kHz but 10kHz works too.

Honestly no simulation will tell you exactly how your board will operate. I'd recommend getting something good on WEBENCH, then make the board and take a bode plot and try some load transients. If it's not working within your specs, move around out those comp values until it does.

-Sam