Inspired from this Application Note: https://www.ti.com/lit/an/slyt293/slyt293.pdf

When designing the buck circuit for the next generation of PicoPD, the maximum input voltage increase from 20V to 28A. However, the output voltage required for the logical portion is the same, 3.3V output. Without worrying about the maximum output current, we have run into another design challenges, minimum on time.

From the application note: "It is usually not possible to derive any arbitrary output voltage from the entire range of permissible input voltages". To better understand this line, lets quickly go over how buck converter operate.

The most basic equation for buck converter is:

Here we assume the efficiency of the converter is 100%. Which mean, all input power, converted to output power. Now, given a fixed Vin, to adjust Vout, we have to adjust the D(duty cycle). At a fixed operate frequency, the duty cycle in percentage can be converted into Ton for the high_side switch.