The DCDCDesigner program suggests an inductor value of 1.2uH for a 5V to 3.3V application, with 2.1A load. I would like to use a 1.0uH inductor that is standard on some other circuits, but am unsure of the downside of using a lower value. Can you advise on this?
This will depend on the DC/DC device used, but in general it will be OK to use a slightly smaller inductor value. It will result in a slightly higher peak-peak inductor current, so it’s important to select an inductor with a high enough saturation rating, in this case greater than 3.0A and even over 3.5A will be required. It’s easy to change the value in DCDC Designer by clicking on the inductor symbol in the schematic, choose another inductor and run the simulation again. You should then see the resulting inductor current, as well as output voltage ripple, gain/bandwidth and margins to make sure those results are acceptable.